#include <bits/stdc++.h>
using namespace std;

int main() {
  int32_t A,B,N,l;
  int32_t max = 0;
  cin >> A >> B >> N;
  l=0;
  for( int32_t i = B-1 ; i <= N ; i+=B){
    int32_t k;
    k = (A*i)/B - A*(l);
    if(N < i){
      break;
    }
    l++;
    if( k > max ){
      max = k;
    }
  }
  cout << max << endl;
}