水题 Codeforces Round #304 (Div. 2) A. Soldier and Bananas

题目传送门

 /*
     水题：ans = (1+2+3+...+n) * k - n，开long long
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 using namespace std;

 typedef long long ll;

 int main(void)        //Codeforces Round #304 (Div. 2) A. Soldier and Bananas
 {
     int k, n, w;
     while (scanf ("%d%d%d", &k, &n, &w) == )
     {
         ll sum = ( + w) * w /  * k;
         if (sum < n)    puts ("");
         else    printf ("%I64d\n", sum - n);
     }

     return ;
 }

 /*
 3 17 4
 */