#include<stdio.h>
#include<math.h>
int main(void){
  int a,b,c,d,e;
  scanf("%d",&a);
  scanf("%d",&b);
  scanf("%d",&c);
  d=b-1;
  if(b-1<=c){
    e=floor(a*d/b)-a*floor(d/b);
    printf("%d",e);
  }else{
    e=floor(a*c/b)-a*floor(c/b);
    printf("%d",e);
  }
  return 0;
}