#include <bits/stdc++.h>
  
#define INF 2000000010
#define mod7 1000000007
#define YJ 1145141919
#define INF_INT_MAX 2147483647
#define INF_LL_MAX 9223372036854775807
#define INF_LL 9223372036854775
#define EPS 1e-10
#define Pi acos(-1)
#define LL long long
#define ULL unsigned long long
#define LD long double 
 
using namespace std;

int main(){

  int S, K;
  cin >> S >> K;
  cout << S%K << endl;

  return 0;
  
}