Problem:
﻿Score: 100 points

Problem Statement

In 2020, AtCoder Inc. with an annual sales of more than one billion yen (the currency of Japan) has started a business in programming education.

One day, there was an exam where a one-year-old child must write a program that prints Hello World, and a two-year-old child must write a program that receives integers A, B and prints A+B.

Takahashi, who is taking this exam, suddenly forgets his age.

He decides to write a program that first receives his age N (1 or 2) as input, then prints Hello World if N=1, and additionally receives integers A, B and prints A+B if N=2.

Write this program for him.

Constraints

N is 1 or 2.

A is an integer between 1 and 9 (inclusive).

B is an integer between 1 and 9 (inclusive).

Input

Input is given from Standard Input in one of the following formats:

1

2
A
B

Output

If N=1, print Hello World; if N=2, print A+B.

Sample Input 1

1

Sample Output 1

Hello World

As N=1, Takahashi is one year old. Thus, we should print Hello World.

Sample Input 2

2
3
5

Sample Output 2

8

As N=2, Takahashi is two years old. Thus, we should print A+B, which is 8 since A=3 and B=5.

Solution in Rust (1.15.1) (judge verdict: Accepted)

//! https://github.com/hatoo/competitive-rust-snippets
//!
//! MIT License
//!
//! Copyright (c) 2018 hatoo
//!
//! Permission is hereby granted, free of charge, to any person obtaining a copy
//! of this software and associated documentation files (the "Software"), to deal
//! in the Software without restriction, including without limitation the rights
//! to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//! copies of the Software, and to permit persons to whom the Software is
//! furnished to do so, subject to the following conditions:
//!
//! The above copyright notice and this permission notice shall be included in all
//! copies or substantial portions of the Software.
//!
//! THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//! IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//! FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//! AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//! LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//! OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//! SOFTWARE.
#![allow(
    unused_imports,
    unused_attributes,
    unused_macros,
    dead_code,
    non_snake_case
)]
use std::cmp::{max, min, Ordering};
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
use std::io::{stdin, stdout, BufWriter, Write};
use std::iter::FromIterator;
#[macro_export]
macro_rules ! get {(@ inner [$ src : expr ] chars ) => {{let mut buf = String :: new () ; $ src . read_line (& mut buf ) . unwrap () ; buf . trim () . chars () . collect ::< Vec < char >> () } } ; (@ inner [$ src : expr ] usize1 ) => {{get ! (@ inner [$ src ] usize ) - 1 } } ; (@ inner [$ src : expr ] [usize1 ] ) => {{get ! (@ inner [$ src ] [usize ] ) . into_iter () . map (| v | v - 1 ) . collect ::< Vec < usize >> () } } ; (@ inner [$ src : expr ] [[usize1 ] ; $ n : expr ] ) => {{(0 ..$ n ) . map (| _ | get ! (@ inner [$ src ] [usize1 ] ) ) . collect ::< Vec < _ >> () } } ; (@ inner [$ src : expr ] [usize1 ; $ n : expr ] ) => {{(0 ..$ n ) . map (| _ | get ! (@ inner [$ src ] [usize1 ] ) ) . flatten () . collect ::< Vec < _ >> () } } ; (@ inner [$ src : expr ] [[chars ] ; $ n : expr ] ) => {{(0 ..$ n ) . map (| _ | get ! (@ inner [$ src ] chars ) ) . collect ::< Vec < _ >> () } } ; (@ inner [$ src : expr ] [chars ; $ n : expr ] ) => {{(0 ..$ n ) . map (| _ | get ! (@ inner [$ src ] chars ) ) . collect ::< Vec < _ >> () } } ; (@ inner [$ src : expr ] [($ ($ tt : tt ) ,* ) ; $ n : expr ] ) => {{(0 ..$ n ) . map (| _ | get ! (@ inner [$ src ] ($ ($ tt ) ,* ) ) ) . collect ::< Vec < _ >> () } } ; (@ inner [$ src : expr ] ($ ($ tt : tt ) ,* ) ) => {{let mut buf : String = String :: new () ; $ src . read_line (& mut buf ) . unwrap () ; let mut iter = buf . split_whitespace () ; ($ (get ! (@ inner_elem_parse [$ tt ] iter . next () . unwrap () ) , ) * ) } } ; (@ inner [$ src : expr ] [$ t : ty ] ) => {{let mut buf = String :: new () ; $ src . read_line (& mut buf ) . unwrap () ; buf . trim () . split_whitespace () . map (| t | t . parse ::<$ t > () . unwrap () ) . collect ::< Vec < _ >> () } } ; (@ inner [$ src : expr ] [[$ t : ty ] ; $ n : expr ] ) => {{(0 ..$ n ) . map (| _ | get ! (@ inner [$ src ] [$ t ] ) ) . collect ::< Vec < _ >> () } } ; (@ inner [$ src : expr ] [$ t : ty ; $ n : expr ] ) => {{(0 ..$ n ) . map (| _ | get ! (@ inner [$ src ] [$ t ] ) ) . flatten () . collect ::< Vec < _ >> () } } ; (@ inner [$ src : expr ] $ t : ty ) => {{let mut buf = String :: new () ; $ src . read_line (& mut buf ) . unwrap () ; buf . trim () . split_whitespace () . next () . unwrap () . parse ::<$ t > () . unwrap () } } ; (@ inner_elem_parse [usize1 ] $ elem : expr ) => {{get ! (@ inner_elem_parse [usize ] $ elem ) - 1 } } ; (@ inner_elem_parse [$ t : ty ] $ elem : expr ) => {{$ elem . parse ::<$ t > () . unwrap () } } ; ($ tt : tt ) => {{use std :: io :: BufRead ; let get_stdin = std :: io :: stdin () ; let mut locked_stdin = get_stdin . lock () ; get ! (@ inner [& mut locked_stdin ] $ tt ) } } ; }
macro_rules ! debug {($ ($ a : expr ) ,* $ (, ) * ) => {# [cfg (debug_assertions ) ] eprintln ! (concat ! ($ ("| " , stringify ! ($ a ) , "={:?} " ) ,*, "|" ) , $ (&$ a ) ,* ) ; } ; }
macro_rules ! echo {($ ($ a : expr ) ,* ) => {let mut s = Vec :: new () ; $ (s . push (format ! ("{}" , $ a ) ) ; ) * println ! ("{}" , s . join (" " ) ) ; } }
#[macro_export]
macro_rules ! chmin {($ base : expr , $ ($ cmps : expr ) ,+ $ (, ) * ) => {{let cmp_min = min ! ($ ($ cmps ) ,+ ) ; if $ base > cmp_min {$ base = cmp_min ; true } else {false } } } ; }
#[macro_export]
macro_rules ! chmax {($ base : expr , $ ($ cmps : expr ) ,+ $ (, ) * ) => {{let cmp_max = max ! ($ ($ cmps ) ,+ ) ; if $ base < cmp_max {$ base = cmp_max ; true } else {false } } } ; }
#[macro_export]
macro_rules ! min {($ a : expr $ (, ) * ) => {{$ a } } ; ($ a : expr , $ b : expr $ (, ) * ) => {{std :: cmp :: min ($ a , $ b ) } } ; ($ a : expr , $ ($ rest : expr ) ,+ $ (, ) * ) => {{std :: cmp :: min ($ a , min ! ($ ($ rest ) ,+ ) ) } } ; }
#[macro_export]
macro_rules ! max {($ a : expr $ (, ) * ) => {{$ a } } ; ($ a : expr , $ b : expr $ (, ) * ) => {{std :: cmp :: max ($ a , $ b ) } } ; ($ a : expr , $ ($ rest : expr ) ,+ $ (, ) * ) => {{std :: cmp :: max ($ a , max ! ($ ($ rest ) ,+ ) ) } } ; }
const BIG_STACK_SIZE: bool = true;
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}
fn solve() {
    let a = get!(usize);
    if a == 1 {
        echo!("Hello World");
    } else {
        let a = get!(usize);
        let b = get!(usize);
        echo!(a + b);
    }
}