#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<ll>>;
ll mod=1e9+7;

int main() {
    ll A,B;
    cin>>A>>B;
    ll an=0;
    if(A==1||B==1){
      cout<<an<<endl;
      return 0;
    }
    for(ll N=1;N<=A*B;N++){
      if(A%N==0&&B%N==0&&N!=1){
        cout<<-1<<endl;
        return 0;
      }
      bool C=true;
      for(ll y=0;y*A<=N;y++){
        if((N-y*A)%B==0)C=false;
      }
      an+=C;
    }
    cout<<an<<endl;
}