#include<bits/stdc++.h>
int gcd(int a,int b){
    if(a%b)return gcd(b,a%b);
    return b;
}
main(){
    int N,D,min;
    scanf("%d%d",&N,&D);
    min = std::min(D,N-D);
    printf("%d\n",D==N?0:N/gcd(N,min)-1);
}