int Calc(int a,int b,int c,int n)
{
	if(a<=0) return b/c*(n+1);
	//这一行千万不要写成if(a<=0) return (n+1)*b/c;不能交换顺序,否则会WA 
   	if(a-c>=0) return n*(n+1)*(a/c)/2+(n+1)*(b/c)+Calc(a%c,b%c,c,n);
   	return (a*n+b)/c*n-Calc(c,c-b-1,a,(a*n+b)/c-1);
}