#include <stdio.h>
#include <stdint.h>
#include <math.h>

int main()
{
  int64_t a, b, n;
  int64_t t;
  scanf("%ld %ld %ld",&a, &b, &n);

  if (n >= b) {
    t = b - 1;
  } else {
    t = n;
  }

  printf("%ld\n", (int64_t)(floor(a*t/b) - a*floor(t/b)));
  return 0;
}

