#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#ifdef __LOCAL
 #include <debug>
#else
 #define debug(...) void(0)
#endif

#define REP(i,n) for(int i=0;i<(n);i++)
#define ALL(v) v.begin(),v.end()

template<typename T>
istream& operator>>(istream&is,vector<T>&v){
  for(T&p:v)is>>p;
  return is;
}
template<typename T>
ostream& operator<<(ostream&os,const vector<T>&v){
  if(&os==&cerr)os<<"[";
  for(int i=0;i<v.size();i++){
    os<<v[i];
    if(i+1<v.size())os<<(&os==&cerr?",":" ");
  }
  if(&os==&cerr)os<<"]";
  return os;
}

using ll=long long;

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  ll n,m;cin>>n>>m;
  ll g=gcd(n,m);
  n/=g;m/=g;
  int tw=0,fi=0;
  while(m%2==0){
    m/=2;
    tw++;
  }
  while(m%5==0){
    m/=5;
    fi++;
  }
  if(m!=1){
    cout<<-1<<endl;
    return 0;
  }
  int mn=min(tw,fi);
  tw-=mn;fi-=mn;
  if(tw){
    while(n%10==0)n/=10;
    while(tw--)(n*=5)%=10;
  }
  else{
    while(n%10==0)n/=10;
    while(fi--)(n*=2)%=10;
  }
  cout<<n%10<<endl;
}