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