{"trustable":true,"prependHtml":"\u003cstyle type\u003d\"text/css\"\u003e\n section pre {\n display: block;\n padding: 9.5px;\n margin: 0 0 10px;\n font-size: 13px;\n line-height: 1.42857143;\n word-break: break-all;\n word-wrap: break-word;\n color: #333;\n background: rgba(255, 255, 255, 0.5);\n border: 1px solid #ccc;\n border-radius: 6px;\n }\n\u003c/style\u003e\n\u003cscript\u003e\n window.katexOptions \u003d {\n delimiters: [\n {left: \u0027\\\\(\u0027, right: \u0027\\\\)\u0027, display: false},\n {left: \u0027\\\\[\u0027, right: \u0027\\\\]\u0027, display: true}\n ]\n };\n\u003c/script\u003e\n","sections":[{"title":"Problem Statement","value":{"format":"HTML","content":"\r\n\u003csection\u003e\r\n\u003cp\u003eThere is a sequence \u003cvar\u003e\\(X\\)\u003c/var\u003e of length \u003cvar\u003e\\(N\\)\u003c/var\u003e, where every element is initially \u003cvar\u003e\\(0\\)\u003c/var\u003e. Let \u003cvar\u003e\\(X_i\\)\u003c/var\u003e denote the \u003cvar\u003e\\(i\\)\u003c/var\u003e-th element of \u003cvar\u003e\\(X\\)\u003c/var\u003e.\u003c/p\u003e\r\n\u003cp\u003eYou are given a sequence \u003cvar\u003e\\(A\\)\u003c/var\u003e of length \u003cvar\u003e\\(N\\)\u003c/var\u003e. The \u003cvar\u003e\\(i\\)\u003c/var\u003e-th element of \u003cvar\u003e\\(A\\)\u003c/var\u003e is \u003cvar\u003e\\(A_i\\)\u003c/var\u003e. Determine if we can make \u003cvar\u003e\\(X\\)\u003c/var\u003e equal to \u003cvar\u003e\\(A\\)\u003c/var\u003e by repeating the operation below. If we can, find the minimum number of operations required.\u003c/p\u003e\r\n\u003cul\u003e\r\n\u003cli\u003eChoose an integer \u003cvar\u003e\\(i\\)\u003c/var\u003e such that \u003cvar\u003e\\(1\\leq i\\leq N-1\\)\u003c/var\u003e. Replace the value of \u003cvar\u003e\\(X_{i+1}\\)\u003c/var\u003e with the value of \u003cvar\u003e\\(X_i\\)\u003c/var\u003e plus \u003cvar\u003e\\(1\\)\u003c/var\u003e.\u003c/li\u003e\r\n\u003c/ul\u003e\r\n\u003c/section\u003e\r\n"}},{"title":"Constraints","value":{"format":"HTML","content":"\r\n\u003csection\u003e\r\n\u003cul\u003e\r\n\u003cli\u003e\u003cvar\u003e\\(1 \\leq N \\leq 2 \\times 10^5\\)\u003c/var\u003e\u003c/li\u003e\r\n\u003cli\u003e\u003cvar\u003e\\(0 \\leq A_i \\leq 10^9(1\\leq i\\leq N)\\)\u003c/var\u003e\u003c/li\u003e\r\n\u003cli\u003eAll values in input are integers.\u003c/li\u003e\r\n\u003c/ul\u003e\r\n\u003c/section\u003e\r\n"}},{"title":"Input","value":{"format":"HTML","content":"\r\n\u003csection\u003e\r\n\u003cp\u003eInput is given from Standard Input in the following format:\u003c/p\u003e\r\n\u003cpre\u003e\u003cvar\u003e\\(N\\)\u003c/var\u003e\r\n\u003cvar\u003e\\(A_1\\)\u003c/var\u003e\r\n\u003cvar\u003e\\(:\\)\u003c/var\u003e\r\n\u003cvar\u003e\\(A_N\\)\u003c/var\u003e\r\n\u003c/pre\u003e\r\n\r\n\u003c/section\u003e\r\n"}},{"title":"Output","value":{"format":"HTML","content":"\r\n\u003csection\u003e\r\n\u003cp\u003eIf we can make \u003cvar\u003e\\(X\\)\u003c/var\u003e equal to \u003cvar\u003e\\(A\\)\u003c/var\u003e by repeating the operation, print the minimum number of operations required. If we cannot, print \u003cvar\u003e\\(-1\\)\u003c/var\u003e.\u003c/p\u003e\r\n\u003c/section\u003e\r\n"}},{"title":"Sample 1","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e4\r\n0\r\n1\r\n1\r\n2\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e3\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\r\n\u003csection\u003e\r\n\r\n\r\n\u003c/section\u003e\r\n\r\n\u003csection\u003e\r\n\r\n\r\n\u003cp\u003eWe can make \u003cvar\u003e\\(X\\)\u003c/var\u003e equal to \u003cvar\u003e\\(A\\)\u003c/var\u003e as follows:\u003c/p\u003e\r\n\u003cul\u003e\r\n\u003cli\u003eChoose \u003cvar\u003e\\(i\u003d2\\)\u003c/var\u003e. \u003cvar\u003e\\(X\\)\u003c/var\u003e becomes \u003cvar\u003e\\((0,0,1,0)\\)\u003c/var\u003e.\u003c/li\u003e\r\n\u003cli\u003eChoose \u003cvar\u003e\\(i\u003d1\\)\u003c/var\u003e. \u003cvar\u003e\\(X\\)\u003c/var\u003e becomes \u003cvar\u003e\\((0,1,1,0)\\)\u003c/var\u003e.\u003c/li\u003e\r\n\u003cli\u003eChoose \u003cvar\u003e\\(i\u003d3\\)\u003c/var\u003e. \u003cvar\u003e\\(X\\)\u003c/var\u003e becomes \u003cvar\u003e\\((0,1,1,2)\\)\u003c/var\u003e.\u003c/li\u003e\r\n\u003c/ul\u003e\r\n\u003c/section\u003e\r\n"}},{"title":"Sample 2","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e3\r\n1\r\n2\r\n1\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e-1\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\r\n\u003csection\u003e\r\n\r\n\r\n\u003c/section\u003e\r\n\r\n\u003csection\u003e\r\n\r\n\r\n\u003c/section\u003e\r\n"}},{"title":"Sample 3","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e9\r\n0\r\n1\r\n1\r\n0\r\n1\r\n2\r\n2\r\n1\r\n2\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e8\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\r\n\u003csection\u003e\r\n\r\n\r\n\u003c/section\u003e\r\n\r\n\u003csection\u003e\r\n\u003c/section\u003e\r\n"}}]}