{"trustable":true,"prependHtml":"\u003cstyle type\u003d\u0027text/css\u0027\u003e\n .input, .output {\n border: 1px solid #888888;\n }\n .output {\n margin-bottom: 1em;\n position: relative;\n top: -1px;\n }\n .output pre, .input pre {\n background-color: #EFEFEF;\n line-height: 1.25em;\n margin: 0;\n padding: 0.25em;\n }\n \u003c/style\u003e\n \u003clink rel\u003d\"stylesheet\" href\u003d\"//codeforces.org/s/96598/css/problem-statement.css\" type\u003d\"text/css\" /\u003e\u003cscript\u003e window.katexOptions \u003d { disable: true }; \u003c/script\u003e\n\u003cscript type\u003d\"text/x-mathjax-config\"\u003e\n MathJax.Hub.Config({\n tex2jax: {\n inlineMath: [[\u0027$$$\u0027,\u0027$$$\u0027], [\u0027$\u0027,\u0027$\u0027]],\n displayMath: [[\u0027$$$$$$\u0027,\u0027$$$$$$\u0027], [\u0027$$\u0027,\u0027$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript type\u003d\"text/javascript\" async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS_HTML-full\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cp\u003eA sequence $$$a_1, a_2, \\dots, a_k$$$ is called an arithmetic progression if for each $$$i$$$ from $$$1$$$ to $$$k$$$ elements satisfy the condition $$$a_i \u003d a_1 + c \\cdot (i - 1)$$$ for some fixed $$$c$$$.\u003c/p\u003e\u003cp\u003eFor example, these five sequences are arithmetic progressions: $$$[5, 7, 9, 11]$$$, $$$[101]$$$, $$$[101, 100, 99]$$$, $$$[13, 97]$$$ and $$$[5, 5, 5, 5, 5]$$$. And these four sequences aren\u0027t arithmetic progressions: $$$[3, 1, 2]$$$, $$$[1, 2, 4, 8]$$$, $$$[1, -1, 1, -1]$$$ and $$$[1, 2, 3, 3, 3]$$$.\u003c/p\u003e\u003cp\u003eYou are given a sequence of integers $$$b_1, b_2, \\dots, b_n$$$. Find any index $$$j$$$ ($$$1 \\le j \\le n$$$), such that if you delete $$$b_j$$$ from the sequence, you can reorder the remaining $$$n-1$$$ elements, so that you will get an arithmetic progression. If there is no such index, output the number \u003cspan class\u003d\"tex-font-style-tt\"\u003e-1\u003c/span\u003e.\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003eThe first line of the input contains one integer $$$n$$$ ($$$2 \\le n \\le 2\\cdot10^5$$$) — length of the sequence $$$b$$$. The second line contains $$$n$$$ integers $$$b_1, b_2, \\dots, b_n$$$ ($$$-10^9 \\le b_i \\le 10^9$$$) — elements of the sequence $$$b$$$.\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003ePrint such index $$$j$$$ ($$$1 \\le j \\le n$$$), so that if you delete the $$$j$$$-th element from the sequence, you can reorder the remaining elements, so that you will get an arithmetic progression. If there are multiple solutions, you are allowed to print any of them. If there is no such index, print \u003cspan class\u003d\"tex-font-style-tt\"\u003e-1\u003c/span\u003e.\u003c/p\u003e"}},{"title":"Examples","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e5\n2 6 8 7 4\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e4\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e8\n1 2 3 4 5 6 7 8\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e1\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e4\n1 2 4 8\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e-1\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"Note","value":{"format":"HTML","content":"\u003cp\u003eNote to the first example. If you delete the $$$4$$$-th element, you can get the arithmetic progression $$$[2, 4, 6, 8]$$$.\u003c/p\u003e\u003cp\u003eNote to the second example. The original sequence is already arithmetic progression, so you can delete $$$1$$$-st or last element and you will get an arithmetical progression again.\u003c/p\u003e"}}]}