#include<stdio.h>
#include<stdlib.h>

int main(void)
{
  long a,b,n,ans,x;
  scanf("%ld %ld %ld",&a,&b,&n);
  if(b < n)
    {
      x = b-1;
    }
  else
    {
      x = n;
    }
  ans = a*x / b;
  printf("%ld\n",ans);
  return 0;
}
