#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
    unsigned long long n, m;
    while (cin>>n>>m) {
        auto g=__gcd(n, m);
        n/=g, m/=g;

        int c2=0, c5=0;
        while (m>0 and m%2==0) { m/=2; ++c2; }
        while (m>0 and m%5==0) { m/=5; ++c5; }

        if (m>1)
            cout<<-1<<endl;
        else {
            while (c5--) n=n*2%10;
            while (c2--) n=n*5%10;
            while (n>0 and n%10==0) n/=10;
            cout<<n%10<<endl;
        }
    }
}