CodeForces-546A-Soldier and Bananas

Description

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 Input

Input

3 17 4

Output

13

一个士兵要买w个香蕉，已经有了n元，然后香蕉第一个k元，第i个k*i元..，问还需要多少钱

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;

typedef long long ll;

int main()
{
    ll k,w,n;
    while(scanf("%lld%lld%lld",&k,&n,&w)!=EOF)
    {
        ll sum=0;
        for(int i =1;i<=w;i++)
          sum +=i*k;
        if(n>=sum)
            printf("0\n");
        else
    printf("%I64d\n",sum-n);
    }
    return 0;
}

.

模拟一下就好了