#include <bits/stdc++.h>
using namespace std;
void fun() {
  int num, n;
  int a, b, k;
  cin >> a >> b >> k;
  int flag = 0, ans = 0;
  int count = 0;
  for (int i = 0; i < b; i++) {
    a = a * 10;
    num = a / b;
    if (num == k) {
      cout << i + 1;
      flag = 1;
      break;
    }
    a = a % b;
  }
  if (flag == 0) {
    cout << "-1";
  }
}
int main() {
  fun();
  return 0;
}
