#include <stdio.h>

long long int gcd( long long int a, long long int b){
	if(b == 0){
		return a;
	}
	
	if(a > b){
		return gcd(b,a%b);
	}else{
		return gcd(a,b%a);
	}
}

int main(void){
	long long int n,m,g, tmp;
	
	
	scanf("%lld", &n);
	scanf("%lld", &m);
	g = gcd(n,m);
	
	n /= g;
	m /= g;
	tmp = m;
	
	while( tmp%2 == 0 ){ tmp/=2;}
	while( tmp%5 == 0 ){ tmp/=5;}
	if(tmp == 1){
		while(n%m != 0){
			while( n>m ){n = n-m;}
			n *= 10;
		}
		n /= m;
		while(n%10==0){n/=10;}
		n = n%10;
		printf("%lld\n", n);
	}else{
		printf("-1\n");
	}
	
	return 0;
}