C :

#include <stdio.h>
int main()
{
    long long n;
    scanf("%lld", &n);
    printf("%lld", (1+n) * n / 2);
    return 0;
}

C++ :

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
long  long f(long n) 
{
long  long sum=((1+n)*n)/2;
return sum;

}
int main()
{

long s=0,m;

	while(scanf("%ld",&m)!=EOF)
	{


printf("%ld\n",f(m));

	}


return 0;

}

Java :

import java.util.Scanner;


public class Main {
	static Scanner sc = new Scanner(System.in);
	public static void main(String[] args){
		Long n = sc.nextLong();
		System.out.println((n*n-n)/2+n);
	}
}