#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;
    while(N%10 == 0) N /= 10;
    if(M != 1){cout << "-1\n"; return 0;}
    swap(m,M);
    while(N%M) N %= M,N *= 10;
    auto answer = N/M;
    cout << answer%10 << endl;
}