#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int (i) = 0 ; (i) < (int)(n) ; (i)++)
#define REP(i,a,b) for(int (i) = a ; (int)(i) <= (int)(b) ; (i)++)
#define all(n) (n).begin(),(n).end()
typedef vector<int> Vi;
typedef vector<Vi> VVi;
typedef pair<int,int> Pii;
typedef vector<Pii> VPii;

int main(){
	long long A,B;
	cin >> A >> B;
	long long G = __gcd(A,B);
	A /= G;
	B /= G;
	if( A % B == 0 ){
		long long T = A / B;
		while( T % 10 == 0 ) T /= 10;
		cout << T % 10 << endl;
		return 0;
	}else{
		A %= B;
		set<long long> used;
		
		__int128 P = A;
		__int128 Q = B;
		
		int ans = 0;
		for(int i = 0 ; P && i < 1000 ; i++){
			if( i == 999 ){
				cout << -1 << endl;
				return 0;
			}
			P = P * 10;
			ans = P / Q;
			P %= Q;
		}
		cout << ans << endl;
	}
	
}