#include <iostream>
int main(){
	uint64_t N,M,m2=0,m5=0;
	std::cin>>N>>M;
	while(M%10==0)M/=10;
	while(M%2==0){M/=2;m2++;}while(M%5==0){M/=5;m5++;}
	if(N%M){std::cout<<-1;return 0;}
	N/=M;N%=10;
	while(m2)N=5;while(m5)N*=2;
	std::cout<<N%10;
}