Codeforces Round #539 (Div. 2)

A. Sasha and His Trip

签。

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 
 4 int n, v;
 5 
 6 int main()
 7 {
 8     while (scanf("%d%d", &n, &v) != EOF)
 9     {
10         int res = 0;
11         if (v >= n - 1) res = n - 1;
12         else
13         {
14             res = v;
15             for (int i = 1, j = 2; i <= n - 1 - v; ++i, ++j)
16                 res += j;
17         }
18         printf("%d\n", res);
19     }
20     return 0;
21 }

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