#include <bits/stdc++.h>
#pragma GCC optimize("03")
using namespace std;
template <typename A, typename B>
ostream &operator<<(ostream &out, pair<A, B> &a) {
  return out << "(" << a.first << ", " << a.second << ")\n";
}
template <typename A>
ostream &operator<<(ostream &out, vector<A> &a) {
  out << "\n[";
  for (int(i) = (int)(0); (i) < (int)((int)a.size()); ++(i)) {
    if (i) out << ", ";
    out << a[i];
  }
  out << "]\n\n";
  return out;
}
void solution() {
  int a, b, c;
  cin >> a >> b >> c;
  int ans = 0;
  for (int(i) = (int)(0); (i) < (int)(100000000); ++(i)) {
    ans++;
    a *= 10;
    if (a / b == c) {
      cout << ans;
      return;
    }
    a %= b;
  }
  cout << -1;
}
int main() {
  ios_base::sync_with_stdio(false);
  solution();
  return 0;
}
