#include <bits/stdc++.h>
using namespace std;
int a, b, c;
template <typename T>
T binary_search(T lower_bound, T upper_bound, bool (*checker)(T)) {
  T middle;
  while (lower_bound < upper_bound) {
    middle = (lower_bound + upper_bound) >> 1;
    if ((*checker)(middle)) {
      upper_bound = middle;
    } else {
      lower_bound = middle + 1;
    }
  }
  return lower_bound;
}
bool checker(int num_secs_waited) { return (num_secs_waited + c) * b >= c * a; }
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cin >> a >> b >> c;
  cout << binary_search(0, (a * c) / b + 10, checker);
  return 0;
}
