C :

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

C++ :

#include<iostream>

using namespace std;

int main()
{
    int a;
    cin>>a;
    cout<<(1+a)*a/2<<endl;
    return 0;
}

Pascal :

var a,b,c:longint;
begin
  readln(a);
  c:=0;
  for b:=1 to a do c:=c+b;
  writeln(c);
end.

Python :

# coding=utf-8
n = int(input())
print((n + 1) * n // 2)