{"problem":{"name":"ModSum","description":{"content":"For an integer $N$, we will choose a permutation ${P_1, P_2, ..., P_N}$ of ${1, 2, ..., N}$. Then, for each $i=1,2,...,N$, let $M_i$ be the remainder when $i$ is divided by $P_i$. Find the maximum pos","description_type":"Markdown"},"platform":"AtCoder","limit":{"time_limit":2000,"memory_limit":262144},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"abc139_d"},"statements":[{"statement_type":"Markdown","content":"For an integer $N$, we will choose a permutation ${P_1, P_2, ..., P_N}$ of ${1, 2, ..., N}$.\nThen, for each $i=1,2,...,N$, let $M_i$ be the remainder when $i$ is divided by $P_i$.\nFind the maximum possible value of $M_1 + M_2 + \\cdots + M_N$.\n\n## Constraints\n\n*   $N$ is an integer satisfying $1 \\leq N \\leq 10^9$.\n\n## Input\n\nInput is given from Standard Input in the following format:\n\n$N$\n\n[samples]","is_translate":false,"language":"English"}],"meta":{"iden":"abc139_d","tags":[],"sample_group":[["2","1\n\nWhen the permutation ${P_1, P_2} = {2, 1}$ is chosen, $M_1 + M_2 = 1 + 0 = 1$."],["13","78"],["1","0"]],"created_at":"2026-03-03 11:01:13"}}