C 参考代码：

#include <stdio.h>
int main() {
    int n;
    while (scanf("%d", &n) != EOF) {
        printf("%d\n", (1 + n) * n / 2);
    }
}

C++ 参考代码：

#include <iostream>
using namespace std;
int main() {
    int n;
    while (cin >> n) {
        cout << (1 + n) * n / 2 << '\n';
    }
}

Java 参考代码：

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int n = sc.nextInt();
            System.out.println((n + 1) * n / 2);
        }
    }
}

Python 参考代码：

while True:
    try:
        n = int(input())
        print((n + 1) * n // 2)
    except:
        break