ModSum

AtCoder

IDabc139_d

Time2000ms

Memory256MB

Difficulty—

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 possible value of $M_1 + M_2 + \cdots + M_N$. ## Constraints * $N$ is an integer satisfying $1 \leq N \leq 10^9$. ## Input Input is given from Standard Input in the following format: $N$ [samples]

Samples

Input #1

Output #1

1

When the permutation ${P_1, P_2} = {2, 1}$ is chosen, $M_1 + M_2 = 1 + 0 = 1$.

Input #2

Output #2

Input #3

Output #3

API Response (JSON)

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      "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",
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    "platform": "AtCoder",
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    "difficulty": "None",
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      "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 pos...",
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      "language": "English"
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