void main() {
	auto N = readLong;
	auto M = readLong;
	long g = gcd(N, M);
	N /= g, M /= g;
	long m = M;
	int cnt2, cnt5;
	while (m % 2 == 0) cnt2++, m /= 2;
	while (m % 5 == 0) cnt5++, m /= 5;
	int ans;
	if (m != 1) {
		ans = -1;
	} else {
		long n = N;
		while (n % 10 == 0) n /= 10;
		n %= 10;
		foreach (i; cnt2 .. cnt5) n = n * 2 % 10;
		foreach (i; cnt5 .. cnt2) n = n * 5 % 10;
		ans = cast(int)n;
	}
	ans.writeln;
}

import std,core.bitop;
string[]_R;
string readString(){while(_R.empty){_R=readln.chomp.split;}auto ret=_R.front;_R.popFront;return ret;}
int readInt(){return readString.to!int;}
long readLong(){return readString.to!long;}
ulong readULong(){return readString.to!ulong;}
real readReal(){return readString.to!real;}
bool chmin(T)(ref T A,T B){if(A>B){A=B;return true;}else{return false;}}
bool chmax(T)(ref T A,T B){if(A<B){A=B;return true;}else{return false;}}
int lowerBound(T)(T[]A,T x){int L=-1,R=cast(int)A.length;while(R-L>1){int mid=(L+R)/2;(A[mid]<x?L:R)=mid;}return R;}
int upperBound(T)(T[]A,T x){int L=-1,R=cast(int)A.length;while(R-L>1){int mid=(L+R)/2;(A[mid]<=x?L:R)=mid;}return R;}