#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#include <random>

using namespace std;

//呪文
#define DUMPOUT cerr
#define dump(...) DUMPOUT<<"  ";DUMPOUT<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"<<endl;DUMPOUT<<"    ";dump_func(__VA_ARGS__)

typedef unsigned uint; typedef long long ll; typedef unsigned long long ull; typedef pair<int, int> pii; typedef pair<ll, ll> pll; typedef pair<double, double> pdd; typedef pair<string, string> pss;
template <typename _KTy, typename _Ty> ostream& operator << (ostream& ostr, const pair<_KTy, _Ty>& m) { ostr << "{" << m.first << ", " << m.second << "}"; return ostr; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& ostr, const map<_KTy, _Ty>& m) { if (m.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { ostr << ", " << *itr; } ostr << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const vector<_Ty>& v) { if (v.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { ostr << ", " << *itr; }	ostr << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const set<_Ty>& s) { if (s.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { ostr << ", " << *itr; }	ostr << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const stack<_Ty>& s) { if (s.empty()) { ostr << "{ }"; return ostr; } stack<_Ty> t(s); ostr << "{" << t.top(); t.pop(); while (!t.empty()) { ostr << ", " << t.top(); t.pop(); } ostr << "}";	return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const list<_Ty>& l) { if (l.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << l.front(); for (auto itr = ++l.begin(); itr != l.end(); ++itr) { ostr << ", " << *itr; } ostr << "}"; return ostr; }
template <typename _KTy, typename _Ty> istream& operator >> (istream& istr, pair<_KTy, _Ty>& m) { istr >> m.first >> m.second; return istr; }
template <typename _Ty> istream& operator >> (istream& istr, vector<_Ty>& v) { for (size_t i = 0; i < v.size(); i++) istr >> v[i]; return istr; }
namespace aux { // print tuple
	template<typename Ty, unsigned N, unsigned L> struct tp { static void print(ostream& os, const Ty& v) { os << get<N>(v) << ", "; tp<Ty, N + 1, L>::print(os, v); } };
	template<typename Ty, unsigned N> struct tp<Ty, N, N> { static void print(ostream& os, const Ty& value) { os << get<N>(value); } };
}
template<typename... Tys> ostream& operator<<(ostream& os, const tuple<Tys...>& t) { os << "{"; aux::tp<tuple<Tys...>, 0, sizeof...(Tys)-1>::print(os, t); os << "}"; return os; }

template<typename A, size_t N, typename T> inline void Fill(A(&array)[N], const T &val) { std::fill((T*)array, (T*)(array + N), val); }

void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) { DUMPOUT << head; if (sizeof...(Tail) == 0) { DUMPOUT << " "; } else { DUMPOUT << ", "; } dump_func(std::move(tail)...); }

#define PI 3.14159265358979323846
#define EPS 1e-11
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define all(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define fake false




template<typename Ty> Ty GCD(Ty m, Ty n)
{
	Ty k;
	do {
		k = m % n;
		m = n; n = k;
	} while (k != 0);
	return m;
}

// FactorInteger(48) = {{2, 4}, {3, 1}};
template<typename KTy, typename Ty> map<KTy, Ty> FactorInteger(KTy n) {
	map<KTy, Ty> mp;
	KTy i;

	while (n % 2 == 0) {
		mp[2]++;
		n /= 2;
	}
	while (n % 5 == 0) {
		mp[5]++;
		n /= 5;
	}
	if (n > 1) mp[n]++;
	return mp;
}

int main()
{
	//clock_t start, end;
	//start = clock();

	cin.tie(0);
	ios::sync_with_stdio(false);

	ll N, M, d;
	cin >> N >> M;
	d = GCD(N, M);
	N /= d; M /= d;

	map<ll, int> fac = FactorInteger<ll, int>(M);
	for (const auto& e : fac) {
		if (e.first != 2 && e.first != 5) {
			cout << -1 << endl;
			return 0;
		}
	}

	while (N % 10 == 0) N /= 10;
	N %= 10;

	int n2 = fac[2], n5 = fac[5];

	if (n2 < n5) {
		for (int i = 0; i < n5 - n2; i++) {
			N *= 2;
			N %= 10;
		}
	}
	else {
		for (int i = 0; i < n2 - n5; i++) {
			N *= 5;
			N %= 10;
		}
	}

	cout << N << endl;

	//end = clock();
	//printf("%d msec.\n", end - start);

	return 0;
}