#include <bits/stdc++.h>

#define ll long long
#define ld long double
#define rep(i,a,b) for (int i = a; i < b; i++)
#define irep(i,a,b) for (int i = a; i > b; i--)
#define print(n) cout << n << endl
#define rup(a,b) (a+b-1)/b
#define end endl;

using namespace std;

unsigned ll gcd(unsigned ll a,unsigned ll b){
    if (a<b){
        swap(a,b);
    }
    if (b==0) return a;
    return gcd(b,a%b);
}
unsigned ll calc(unsigned ll N){
            string s = to_string(N);
        char now1 = '1';
        rep(i,0,s.size()){
            if (s[i]=='0'){
                continue;
            }
            now1 = s[i];
        }
        return (unsigned ll)(now1-'0');
}
int main(){
    cout << fixed << setprecision(15);
    
    unsigned ll N,M;
    cin>>N>>M;

    unsigned ll d;

    bool p = false;

    d = gcd(N,M);
    N /= d;
    M /= d;
    unsigned ll now = 1;
    int count = 0;
    while(true){
        count ++ ;
        if (count>=100) break;
        d = gcd(M,10);
        if (d==1) break;
        M /= d;
        now *= (10/d);
        now = calc(now);
        //cout<<now<<" "<<M<<end;
        }

    if (M == 1){
        string s = to_string(N);
        char now1 = '1';
        rep(i,0,s.size()){
            if (s[i]=='0'){
                continue;
            }
            now1 = s[i];
        }
        N = now * (int)(now1-'0');
        //cout<<now<<" "<<N<<" "<<(int)(now1-'0')<<endl;
        s = to_string(N);
        now1 = '1';
        rep(i,0,s.size()){
            if (s[i]=='0'){
                continue;
            }
            now1 = s[i];
        }print(now1);
    }else{
        print(-1);
    }
    //system("pause");
    return 0;
}