#include <bits/stdc++.h>
using namespace std;
int numr, denr, c;
void fractionToDecimal(int numr, int denr) {
  string res;
  map<int, int> mp;
  mp.clear();
  int rem = numr % denr;
  int ans = 0;
  while ((rem != 0) && (mp.find(rem) == mp.end())) {
    mp[rem] = res.length();
    rem = rem * 10;
    int res_part = rem / denr;
    if (res_part == c) {
      cout << ans + 1 << endl;
      exit(0);
    }
    rem = rem % denr;
    ans++;
  }
  if (rem == 0 && c == 0)
    cout << ans + 1 << endl;
  else
    cout << -1 << endl;
}
int main() {
  cin >> numr >> denr >> c;
  fractionToDecimal(numr, denr);
  return 0;
}
