#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

ull gcd(ull a, ull b) {
	if (b == 0) return a;
	return gcd(b, a % b);
}

ull lcm(ull a, ull b) {
	return a / gcd(a, b) * b;
}

int main() {
	ull n, m;
	cin >> n >> m;
	
	ull g = gcd(n, m);
	n /= g; m /= g;
	
	stringstream ss;
	ss << n / m;
	string str = ss.str();
	
	int last = 0;
	REP(i, str.size()) if (str[i] != '0') last = str[i] - '0';
	
	n %= m;
	
	REP(i, 100) {
		ull tmp = n;
		int d = 0;
		
		n = 0;
		REP(j, 10) {
			n += tmp;
			if (n >= m) {
				n -= m;
				d++;
			}
		}
		if (d != 0) last = d;
	}
	
	if (n) last = -1;
	cout << last << endl;
	
	return 0;
}