C :

#include<stdio.h>
int main()
{int i,n;
int s=0;
scanf("%d",&n);
for(i=n;i>0;i--)
{s=s+i;} 
printf("%d",s);
return 0;
 } 

Java :

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int sum = 0;
		for(int i=n;i>0;i--) {
			sum = sum+i;
		}
		System.out.println(sum);
	}

}