#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(LL i = a;i<b; i++)
#define rrep(i,a,b) for(LL i = a;i>b; i--)
#define INF ((1LL<<62)-(1LL<<31))
#define ooki 9,223,372,036,854,775,807
#define tii -9,223,372,036,854,775,808
typedef long long LL;
int main(){
 LL s,k;
  cin >> s >>  k;
  cout<<s%k<<endl;
}