C :

#include<stdio.h>
#define MOD(x,y) x%y
main()
{
  int a,b;
  scanf("%d%d",&a,&b);
  printf("%d\n",MOD(a,b));
}

C++ :

#include<bits/stdc++.h>
using namespace std;
long long a,b;
int main()
{
	cin>>a>>b;
	cout<<a%b;
		
    return 0;
}