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

-----Output-----
Print the maximum possible value of $M_1 + M_2 + \cdots + M_N$.

-----Sample Input-----
2

-----Sample Output-----
1

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

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