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

int main(void) {
  unsigned long int a, b, n;
  scanf("%ld %ld %ld", &a, &b, &n);
  unsigned long int x, max=0;
  unsigned long int tmp;
  for(x=1; x<=n; x++) {
    tmp = (unsigned long int)(floor(a*x/b) - a*floor(x/b));
    if(tmp > max) {
      max = tmp;
    }
  }
  printf("%ld\n", max);
  return 0;
}
