#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP(i,(int)(n)-1,0)
#define REP(i,s,e) for (i = s; i <= e; i++)
#define rep(i,n) REP(i,0,(int)(n)-1)
#define INF 100000000

typedef long long ll;

int main() {
    int i;
    ll n, m;
    cin >> n >> m;
    rep (i,100) {
        if (n % m == 0) {
            ll ret = n / m;
            while (ret % 10 == 0)
                ret /= 10;
            cout << ret % 10 << endl;
            return 0;
        }
        n = n % m * 10;
    }
    cout << -1 << endl;
    return 0;
}