CF 546A-Soldier and Bananas

CF 546A
A. Soldier and Bananas

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

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.

Examples

input

3 17 4

output

13

题意：有W个香蕉，第一个k元，第二个2k元，第三个3k元......现在有n元，还需要多少元。

思路：水。

#include<stdio.h>

#include<math.h>

int main()

{

    int k,n,w,i,t;//k danjia n qian w geshu

91bc
    scanf("%d%d%d",&k,&n,&w);

    for(i=1;i<=w;i++)

    {

        t=i*k;

        n-=t;

    }

    if(n<0) printf("%d\n",-n);

    else printf("0\n");

    return 0;

}