Problem:
Score : 100 points

Problem Statement

There are N children in AtCoder Kindergarten. Mr. Evi will arrange the children in a line, then give 1 candy to the first child in the line, 2 candies to the second child, ..., N candies to the N-th child. How many candies will be necessary in total?

Constraints

1≦N≦100

Input

The input is given from Standard Input in the following format:

N

Output

Print the necessary number of candies in total.

Sample Input 1

3

Sample Output 1

6

The answer is 1+2+3=6.

Sample Input 2

10

Sample Output 2

55

The sum of the integers from 1 to 10 is 55.

Sample Input 3

1

Sample Output 3

1

Only one child. The answer is 1 in this case.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Math;
using static ConsoleApplication.Utils;

namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var n = ReadInt();
            var res = Enumerable.Range(1, n).Sum();
            WriteLine(res);
        }
    }

    public static class Utils
    {
        #region Extensions for IO

        public static int ReadInt()
            => ReadInts().First();

        public static IEnumerable<int> ReadInts()
            => ReadStrings().Select(int.Parse);

        public static IEnumerable<String> ReadStrings()
            => ReadLine().Split(' ');

        #endregion

        #region Extensions of int

        public static bool IsOdd(this int n)
            => !n.IsEven();

        public static bool IsEven(this int n)
            => n % 2 == 0;

        public static bool CanDivideWith(this int n, int divisor)
            => n % divisor == 0;

        #endregion

        #region Extensions of string

        public static int ToInt(this string str)
            => int.Parse(str);

        public static long ToLong(this string str)
            => long.Parse(str);

        public static bool IsNullOrEmpty(this string str)
            => string.IsNullOrEmpty(str);

        #endregion

        public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
        {
            foreach (var item in source)
            {
                action(item);
            }
        }

        public static IEnumerable<T> Peek<T>(this IEnumerable<T> source, Action<T> action)
        {
            foreach (var item in source)
            {
                action(item);
            }
            return source;
        }
    }
}