/******************************************************************************
Online C Compiler.
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*******************************************************************************/
#include <stdio.h>
void main()
{
int i,n,sum=0;
printf("n: ");
scanf("%d",&n);
if(n<0)
printf("invalid value of n\n");
else
{
for(i=0;i<=n;i++)
sum=sum+i;
}
printf("sum:%d",sum);
}