#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>
#include <numeric>
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
constexpr long long MAX = 5100000;
constexpr long long INF = 1LL << 60;
constexpr int inf = 1000000007;
constexpr long long mod = 1000000007LL;
//constexpr long long mod = 998244353LL;
const long double PI = acos((long double)(-1));

using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;

int main()
{
    /*
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    */
    ull n, m; cin >> n >> m;;
    ull g = gcd(n, m);
    n /= g;
    m /= g;
    ull t = m;
    ull cnt2 = 0;
    ull cnt5 = 0;
    while (t % 2 == 0) t /= 2, cnt2++;
    while (t % 5 == 0) t /= 5, cnt5++;
    while (n % 10 == 0) n /= 10;
    if (t != 1) puts("-1");
    else {
        while (cnt2 < cnt5) {
            n *= 2;
            while (n % 10 == 0) n /= 10;
            n %= 10;
            cnt2++;
        }
        while (cnt5 < cnt2) {
            n *= 5;
            while (n % 10 == 0) n /= 10;
            n %= 10;
            cnt5++;
        }
        cout << n % 10 << endl;
    }
    return 0;
}