#include <bits/stdc++.h>
using namespace std;
//#include <atcoder/all>
//using namespace atcoder;
using ll=long long;
using Graph=vector<vector<int>>;
#define MAX 1000000
#define MOD 1000000009
//#define MOD 998244353
#define INF 1000000000
//#define INF 1000000000000000000

ll gcd(ll A,ll B){
  while(A%B!=0){
    ll tmp=A%B;
    A=B;
    B=tmp;
  }
  return B;
}

int main(){
  ll N,M;
  cin>>N>>M;
  ll g=gcd(N,M);
  N/=g;
  M/=g;
  if(M==1){
    while(N%10==0){
      N/=10;
    }
    cout<<N%10<<endl;
    return 0;
  }

  while(M%10==0){
    M/=10;
  }
  int cnt2=0;
  int cnt5=0;
  while(M%2==0){
    cnt2++;
    M/=2;
  }
  while(M%5==0){
    cnt5++;
    M/=5;
  }
  if(M>1){
    cout<<-1<<endl;
    return 0;
  }

  if(cnt2>0){
    cout<<5<<endl;
  }else{
    ll x=N%10;
    for(int i=0;i<cnt5;i++){
      x%=5;
      x*=2;
    }
    cout<<x<<endl;
  }
}