#include<stdio.h>
int main(){
  int a;
  unsigned long int b,n;
  int max=0;
  int tmp=0;
  scanf("%d %ld %ld",&a,&b,&n);
  for(int i=0;i<=n;i++){
    tmp=(int)(a*i/b)-a*(int)(i/b);
    if(tmp>max){
      max=tmp;
    }
  }
  printf("%d",max);
  return 0;
}
