CF 546A Soldier and Bananas

Descripe

A soldier wants to buy w bananas in the shop. He has to pay k dollars for the first banana, 2k dollars for the second one and so on (in other words, he has to pay i·k dollars for the i-th banana).

He has n dollars. How many dollars does he have to borrow from his friend soldier to buy w bananas?

Input

The first line contains three positive integers k, n, w (1  ≤  k, w  ≤  1000, 0 ≤ n ≤ 10⁹), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants.

Output

Output one integer — the amount of dollars that the soldier must borrow from his friend. If he doesn't have to borrow money, output 0.

Sample test(s)

Input

3 17 4

Output

13

Div2 A， 简单模拟计算
CODE:

#include <iostream>
#include <cstdio>
#include <cstring>
#define REP(i, s, n) for(int i = s; i <= n; i ++)
#define REP_(i, s, n) for(int i = n; i >= s; i --)

using namespace std;

int main(){
    int k, n, w;
    scanf("%d%d%d", &k, &n, &w);
    int sum = 0;
    REP(i, 1, w)
        sum += i * k;
    
    if(sum > n) printf("%d\n", sum - n);
    else printf("0\n");
    return 0;
}