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

C++ :

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