#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <cctype>
#include <tuple>
#include <climits>
#include <bitset>
#include <cassert>
#include <random>

#ifdef _MSC_VER
#include <agents.h>
#endif

#define FOR(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep(i, n) FOR(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define REV(v) v.rbegin(), v.rend()
#define MEMSET(v, s) memset(v, s, sizeof(v))
#define UNIQUE(v) (v).erase(unique(ALL(v)), (v).end())
#define MP make_pair
#define MT make_tuple

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

template<class T> inline void chmax(T& a, const T& b) { if (b > a) a = b; }
template<class T> inline void chmin(T& a, const T& b) { if (b < a) a = b; }

const double EPS = 1e-9;

ll gcd(ll m, ll n){
	return n ? gcd(n, m%n) : m;
}

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	ll n, m;
	cin >> n >> m;

	//m = 1ll << 62;
	//n = m - 1;
	//cout << n << endl;

	ll g = gcd(n, m);
	n /= g, m /= g;

	ll x = m;
	for (auto e : { 2, 5 })while (x % e == 0) x /= e;
	
	if (x == 1){
		if (n%m == 0) {
			ll x = n / m;
			while (x % 10 == 0) x /= 10;
			cout << to_string(x).back() << endl;
		}
		else{
			ll x = n % 10;

			while (m != 1){
				for (auto e : { 2, 5 }){
					if (m % e == 0) m /= e;
					else x = x * e % 10;
				}
			}
			cout << x << endl;
		}
	}
	else cout << -1 << endl;

	return 0;
}