Sum of n+(n-1)+(n-2)+...4+3+2+1 using C language

#include<stdio.h>
int main()
{
 int a,n,sum=0;
 printf("enter the value of n :");
 scanf("%d",&n);
 for(a=n;a>=1;a--)
 {
  sum=sum+a;
 }
 printf("The sum is :%d",sum);
 return 0;
}