#include "bits/stdc++.h"
using namespace std;
#define FOR(i,a,b) for(int i =(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define REPm(i,n) for(int i=(n)-1;i>=0;i--)
#define REP1(i,n) for(int i=1;i<=(n);i++)
#define mp make_pair
typedef long long ll;
ll gcd(ll a,ll b){
    if(b == 0) return a;
    else gcd(b,a%b);
}
int main(){
    ll N,M;
    cin >> N >> M;
    ll g = gcd(N,M);
    N /= g;
    M /= g;
    int count2 = 0;
    int count5 = 0;
    while(M%2 == 0){
        count2++;
        M /= 2;
    }
    while(M%5 == 0){
        count5++;
        M /= 5;
    }
    int ans;
    if(M > 1) ans = -1;
    else{
        while(N%10 == 0) N /= 10;
        ans = N%10;
        if(count2 > count5) ans = (ans*5)%10;
        if(count2 < count5){
            REP(i,(count5-count2-1)%4+1) ans = (ans*2)%10;
        }
    }
    cout << ans << endl;
    return 0;
}