> here is my source (C++):
---------------------------
#include <stdio.h>

int i;long sum=0;
int n;

void main()
 {
  scanf("%d",&n);
  if(n<1)
   for(i=1;i>=n;i--)
    sum+=i;
  else
   for(i=1;i<=n;i++)
    sum+=i;
  printf("%ld",sum);
 }
--------------------------

Try to delete  void  because  i did so , and my programm was right good Luck !