#include <stdio.h>

int main(void)
{
  long long  a, b, n;
  int s[1000000000000];
  int max = 0;
  int tmp;

  scanf("%lld %lld %lld", &a, &b, &n);

  for (long long i = 0; i <= n; i++){
    s[i] = (a * i) / b - a * (i / b);
  }

  for (int i = 0; i <= a; i++){
    if (max < s[i]) max = s[i];
  }

  printf("%d", max);

  return 0;
}