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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class Main {
	static boolean bElapsed = false;
	List<String> list = new ArrayList<>();
	Set<String> set = new HashSet<>();
	Map<String,String> map = new HashMap<>();

	void solve(BufferedReader br) throws Exception {
		String line = br.readLine();
		int n = Integer.parseInt(line);
		long sum = n*(n+1)/2;
		pln(sum);
	}

	void p(char c) {
		System.out.print(c);
	}
	void pln(char c) {
		System.out.println(c);
	}
	void p(long l) {
		System.out.print(l);
	}
	void pln(long l) {
		System.out.println(l);
	}
	void p(String s) {
		System.out.print(s);
	}
	void pln(String s) {
		System.out.println(s);
	}
	public static void main(String[] args) throws Exception {
		long start = System.currentTimeMillis();
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		new Main().solve(br);
		long end = System.currentTimeMillis();
		if (bElapsed) {
			System.out.println((end-start) + "ms");
		}
	}
}