#include <stdio.h>

int main()
{
  int a, b, n;
  int i, max, temp;
  scanf("%d %d %d", &a, &b, &n);
  for (i = 0; i <= n; i++) {
    temp = (a*i/b)-a*(i/b);
    if (temp > max)
      max = temp;
  }
  printf("%d\n", max);
}
