{"problem":{"name":"Sequence Growing Easy","description":{"content":"There is a sequence $X$ of length $N$, where every element is initially $0$. Let $X_i$ denote the $i$\\-th element of $X$. You are given a sequence $A$ of length $N$. The $i$\\-th element of $A$ is $A_i","description_type":"Markdown"},"platform":"AtCoder","limit":{"time_limit":2000,"memory_limit":262144},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"agc024_c"},"statements":[{"statement_type":"Markdown","content":"There is a sequence $X$ of length $N$, where every element is initially $0$. Let $X_i$ denote the $i$\\-th element of $X$.\nYou are given a sequence $A$ of length $N$. The $i$\\-th element of $A$ is $A_i$. Determine if we can make $X$ equal to $A$ by repeating the operation below. If we can, find the minimum number of operations required.\n\n*   Choose an integer $i$ such that $1\\leq i\\leq N-1$. Replace the value of $X_{i+1}$ with the value of $X_i$ plus $1$.\n\n## Constraints\n\n*   $1 \\leq N \\leq 2 \\times 10^5$\n*   $0 \\leq A_i \\leq 10^9(1\\leq i\\leq N)$\n*   All values in input are integers.\n\n## Input\n\nInput is given from Standard Input in the following format:\n\n$N$\n$A_1$\n$:$\n$A_N$\n\n[samples]","is_translate":false,"language":"English"}],"meta":{"iden":"agc024_c","tags":[],"sample_group":[["4\n0\n1\n1\n2","3\n\nWe can make $X$ equal to $A$ as follows:\n\n*   Choose $i=2$. $X$ becomes $(0,0,1,0)$.\n*   Choose $i=1$. $X$ becomes $(0,1,1,0)$.\n*   Choose $i=3$. $X$ becomes $(0,1,1,2)$."],["3\n1\n2\n1","\\-1"],["9\n0\n1\n1\n0\n1\n2\n2\n1\n2","8"]],"created_at":"2026-03-03 11:01:14"}}