sicily 1001. Black Magic

#include<stdio.h>
#include<string.h>
int main()
{
int _case;
int n,m,k;

scanf("%d",&_case);
while(_case--)
{
scanf("%d %d %d",&n,&m,&k);
int t,sum=0;
//k=p;
for(t=n;t>=0;t-=m)
{
sum+=t;
if(k-sum<=0)break;
}
//printf("%d %d\n",sum,t);
if(t>=0)printf("%d\n",n-(sum-k));
else printf("0\n");
}
return 0;
}