#include<bits/stdc++.h>
using namespace std;
int main(){
  int n,d,nc,dc;
  cin >> n >> d;
  if(d == 0){
    printf("0\n");
  }else{
    nc = n;dc = d;
    while(nc!=dc){
      if(nc>dc)nc-=dc;
      else dc-=nc;
    }
    printf("%d\n",n-((dc-1)*(n/dc)+1));
  }
}