#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#define rep(i,n) for(int i = 0;i < n;i++)
#define REP(i,n,k) for(int i = n;i < k;i++)
#define P(p) cout<<(p)<<endl;
#define pi 3.1415926535
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
int dx[] = { 0, 1, 0, -1 };
int dy[] = { -1, 0, 1, 0 };

unsigned long long sttoi(std::string str) {
	unsigned long long ret;
	std::stringstream ss; ss << str;
	ss >> ret;
	return ret;
}

ull gcd(ull a, ull b){
	if (b > a)swap(a, b);
	if (b == 0) return a;
	return gcd(b, a%b);
}
ll f[] = { 3, 5, 17, 257, 65537 };
void solve() {
	ull n, m;
	cin >> n >> m;
	ull g = gcd(n, m);
	n /= g;
	m /= g;
	ull tmp = m;
	while (tmp % 2 == 0){
		tmp /= 2;
	}
	while (tmp % 5 == 0){
		tmp /= 5;
	}
	if (tmp == 1){
		cout << setprecision(20) << fixed;
		string ans = to_string(((double)n / (double)m)*10000000000000000);
		for (int i = ans.length()-1; i >= 0; i--){
			if (ans[i] != '0' && ans[i] != '.'){
				P(ans[i]);
				return;
			}
		}
	}
	else{
		P(-1);
	}
}

int main() {
	solve();
	return 0;
}