#include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
ll gcd (ll a,ll b){
    return b ? gcd(b,a%b) : a;
}
void divgcd(ll &N,ll &M){
    ll g = gcd(N,M);
    N /= g,M /= g;
}
main(){
    ll N,M;
    cin >> N >> M;
    divgcd(N,M);
    ll k = M;
    int p[] = {2,5},cnt[2] = {};
    rep(i,2){
        while(k % p[i] == 0){
            k /= p[i];
            cnt[i]++;
        }
    }
    if(k != 1){
        cout << -1 << endl;
        return 0;
    }
    int num = N % 10;
    if(!num){
        while(!num){
            N /= 10;
            num = N % 10;
        }
    }
    bool flag = cnt[0] > cnt[1];
    //|2 - 5| 大きい方をかける回数
    while(cnt[0] != cnt[1]){
        num = (num * p[flag]) % 10;
        cnt[flag]++;
    }
    
    cout << num << endl;
}