CodeForces-546A-Soldier and Bananas

Description

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

He has n dollars. How many dollars does he have to borrow from his friend soldier to buyw 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, output0.

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;}

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模拟一下就好了