#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef unsigned long long ULL;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(auto i: c)
#define SORT(c) sort((c).begin(),(c).end())

#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()

const double EPS = 1e-10;
const double PI  = acos(-1.0);

#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

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

	LL N, M;
	cin >> N >> M;

	function<LL(LL, LL)> gcd = [&](LL m, LL n){
		if(m < n) swap(m, n);
		if(n == 0) return m;
		return gcd(n, m % n);
	};

	LL m = M / gcd(M, N), n = N / gcd(M, N);

	LL tmp = m, nTwo = 0, nFive = 0;
	while(tmp % 2 == 0){
		tmp /= 2;
		nTwo++;
	}
	while(tmp % 5 == 0){
		tmp /= 5;
		nFive++;
	}
	while(n % 10 == 0) n /= 10;
	if(tmp != 1) cout << -1 << endl;
	else{
		LL ret = n;
		while(nTwo < nFive){
			ret = (ret * 2) % 10;
			nFive--;
		}
		while(nTwo > nFive){
			ret = (ret * 5) % 10;
			nTwo--;
		}

		cout << ret % 10 << endl;
	}


	return 0;
}