#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()

using namespace std;

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

int main()
{
	ios_base::sync_with_stdio(0);
	ll N, M; cin >> N >> M;
	ll g = __gcd (N, M );
	N /= g;
	M /= g;
	int p2 = 0, p5 = 0;

	while (M % 2LL == 0 ) M /= 2LL, p2++;
	while (M % 5LL == 0 ) M /= 5LL, p5++;

	while (N % 10 == 0 ) N /= 10;
	N %= 10;
	
	while (p2 > p5 ) p5++, N = ((N*5LL) % 10LL );
	while (p2 < p5 ) p2++, N = ((N*2LL) % 10LL );

	if (M != 1LL ){
		cout << -1 << endl;
	}else{
		cout << N << endl;
	} // end if

	return 0;
}