#define _USE_MATH_DEFINES
 
#include <iostream>
#include <iomanip>
#include <sstream>
 
#include <algorithm>
#include <cmath>
 
#include <string>
//#include <array>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>
#include <map>
 
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
 
#define PII pair<int,int>
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////
LL gcd(LL a,LL b){
	while( b != 0){
		a = a % b;
		swap(a,b);
	}
	return a;
}
int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    //cout << setprecision(16);//
	
	//解説見た
	LL N,M;
	cin>>N>>M;
	LL gcdNum = gcd(N,M);
	N /= gcdNum;
	M /= gcdNum;

	if( M == 1){
		while(N % 10 == 0){
			N /= 10;
		}
		P(N%10);
		return 0;
	}
	int count2=0;
	int count5=0;
	while( M%2 == 0){
		M /= 2;
		++count2;
	}
	while( M%5 == 0){
		M /= 5;
		++count5;
	}
	if( M != 1){
		P(-1);
		return 0;
	}
	while(N % 10 == 0){N /= 10;}
	if( count2 < count5){
		//count5-count2回2/2を掛ける
		rep(i,count5-count2){
			N *= 2;
			while(N % 10 == 0){N /= 10;}
			N = N % 1000;
		}
	}else{
		rep(i,count2-count5){
			N *= 5;
			while(N % 10 == 0){N /= 10;}
			N = N % 1000;
		}
	}

	P(N%10);
	return 0;
}