There are N children

就是个累加的过程，非常基础。

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();int sum = 0;for (int i = 1; i <= n; i++) {
    sum = sum + i;}System.out.println(sum);}}
}