#include <iostream>
#include <set>
using namespace std;
typedef unsigned long long ull;
ull gcd(ull n, ull m){return m?gcd(m,n%m):n;}
int main(){
    ull N,M;
    cin >> N >> M;

    ull g = gcd(N,M);
    N /= g; M /= g;

    if(M == 1){
        while(N > 0 && N%10 == 0) N /= 10;
        cout << N%10 << endl;
    } else {
        int p2 = 0, p5 = 0;
        ull m = M;
        while(m % 2 == 0) m /= 2, p2++;
        while(m % 5 == 0) m /= 5, p5++;
        if(m != 1){
            cout << -1 << endl;
        } else {
            while(p2 > 0 && p5 > 0) p2--,p5--;
            N %= 10;
            while(p2 || p5){
                if(p2) N *= 5, p2--;
                if(p5) N *= 2, p5--;
	            N %= 10;
            }
            cout << N << endl;
        }
    }
    return 0;
}