#include <iostream>
int main(){
	uint64_t N,M;int m2=0;
	std::cin>>N>>M;
	while(M%2==0){M/=2;m2++;}while(M%5==0){M/=5;m2--;}
	if(N%M){std::cout<<-1;return 0;}
	N/=M;
	while(N%10==0)N/=10;
	while(N%2==0){N/=2;m2--;}while(N%5==0){N/=5;m2++;}N%=10;
	if(m2>0)N=5;else while(m2++)N*=2;
	std::cout<<N%10;
}