codeforces 546A solution

cdf546A.c

#include<stdio.h>
int main()
{
    int n , k ,w;
    int i ,sum = 0;
    int dollar;
    scanf("%d %d %d",&k,&n,&w);
    for(i = 1;i <= w;i++)
    {
        sum = sum + i*k;
    }
    dollar =  sum - n;
    if(dollar > 0)
    {
        printf("%d\n",dollar);
    }
    else
    printf("0\n");
    return 0;

}