#include <stdio.h>

int main(void){

  long a,b,n;
  scanf("%ld %ld %ld", &a, &b, &n);
  long x = b-1;
  if (x > n) {
    x = n;
  }
  long answer = a*x/b-a*(x/b);
  printf("%ld\n", answer);

  return 0;
}