#include <bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
 
    unsigned long long N,M; cin >> N >> M;
    auto g = gcd(N,M);
    N /= g; M /= g;
    auto m = M;
    while(M%2 == 0) M /= 2;
    while(M%5 == 0) M /= 5;
    if(M != 1){cout << "-1\n"; return 0;}
    swap(m,M);
    while(N%10 == 0) N /= 10;
    while(M%10 == 0) M /= 10;
    
    if(M == 1) cout << N%10 << endl;
    else if(M%2 == 0){
        while(N%2 == 0) N /= 2;
        cout << N%10*5%10 << endl;
    }    
    else{
        while(N%5 == 0) N /= 5;
        int log5 = 0;
        while(M%5 == 0) log5++,M /= 5;
        log5 %= 4;
        if(log5 == 0) cout << N%10*6%10 << endl;
        if(log5 == 1) cout << N%10*2%10 << endl;
        if(log5 == 2) cout << N%10*4%10 << endl;
        if(log5 == 3) cout << N%10*8%10 << endl;
    }
}