{"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$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript type\u003d\"text/javascript\" async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS_HTML-full\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cp\u003eThe sequence of integers $$$a_1, a_2, \\dots, a_k$$$ is called a good array if $$$a_1 \u003d k - 1$$$ and $$$a_1 \u0026gt; 0$$$. For example, the sequences $$$[3, -1, 44, 0], [1, -99]$$$ are good arrays, and the sequences $$$[3, 7, 8], [2, 5, 4, 1], [0]$$$ — are not.\u003c/p\u003e\u003cp\u003eA sequence of integers is called good if it can be divided into a positive number of good arrays. Each good array should be a subsegment of sequence and each element of the sequence should belong to exactly one array. For example, the sequences $$$[2, -3, 0, 1, 4]$$$, $$$[1, 2, 3, -3, -9, 4]$$$ are good, and the sequences $$$[2, -3, 0, 1]$$$, $$$[1, 2, 3, -3 -9, 4, 1]$$$ — are not.\u003c/p\u003e\u003cp\u003eFor a given sequence of numbers, count the number of its \u003cspan class\u003d\"tex-font-style-bf\"\u003esubsequences\u003c/span\u003e that are good sequences, and print the number of such subsequences modulo \u003cspan class\u003d\"tex-font-style-bf\"\u003e998244353\u003c/span\u003e.\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003eThe first line contains the number $$$n~(1 \\le n \\le 10^3)$$$ — the length of the initial sequence. The following line contains $$$n$$$ integers $$$a_1, a_2, \\dots, a_n~(-10^9 \\le a_i \\le 10^9)$$$ — the sequence itself.\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003eIn the single line output one integer — the number of subsequences of the original sequence that are good sequences, taken modulo \u003cspan class\u003d\"tex-font-style-bf\"\u003e998244353\u003c/span\u003e.\u003c/p\u003e"}},{"title":"Examples","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e3\n2 1 1\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e2\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e4\n1 1 1 1\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e7\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"Note","value":{"format":"HTML","content":"\u003cp\u003eIn the first test case, two good subsequences — $$$[a_1, a_2, a_3]$$$ and $$$[a_2, a_3]$$$.\u003c/p\u003e\u003cp\u003eIn the second test case, seven good subsequences — $$$[a_1, a_2, a_3, a_4], [a_1, a_2], [a_1, a_3], [a_1, a_4], [a_2, a_3], [a_2, a_4]$$$ and $$$[a_3, a_4]$$$.\u003c/p\u003e"}}]}