#include <bits/stdc++.h>

#define REP(i, x, n) for(int i = x; i < (int)(n); i++)
#define rep(i, n) REP(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define F first
#define S second
#define mp make_pair

using namespace std;

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

int main() {
  // ios_base::sync_with_stdio(false);
  ull N, M;
  cin >> N >> M;

  if(N % M == 0) {
    ull ans = N / M;
    while(ans % 10 == 0) ans /= 10;
    cout << ans % 10 << endl;
  }
  else {
    set<pair<ull, int>> d;
    N %= M;
    int ans = 0;
    while(N % M) {
      while(N < M) N *= 10;
      int v = N / M;
      if(d.count(mp(N, v))) {
        ans = -1;
        break;
      }
      d.insert(mp(N, v));
      ans = v;
      N %= M;
    }
    cout << ans << endl;
  }
    
  return 0;
}