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)

fn programming_education() -> Result<String, &'static str> {                                                                                                                  
    let mut input = String::new();                                                                                                                                            
    std::io::stdin().read_line(&mut input)                                                                                                                                    
        .map_err(|e| "input N error.")?;                                                                                                                                      
    let n : i32 = input.trim_right().parse()                                                                                                                                  
        .map_err(|e| "parse N error.")?;                                                                                                                                      
                                                                                                                                                                              
    if n == 1 {                                                                                                                                                               
        Ok(String::from("Hello World"))                                                                                                                                       
    }                                                                                                                                                                         
    else {                                                                                                                                                                    
        let mut input = String::new();                                                                                                                                        
        std::io::stdin().read_line(&mut input)                                                                                                                                
            .map_err(|e| "input A error.")?;                                                                                                                                  
        let a : i32 = input.trim_right().parse()                                                                                                                              
            .map_err(|e| "parse A error.")?;                                                                                                                                  
        let mut input = String::new();                                                                                                                                        
        std::io::stdin().read_line(&mut input)                                                                                                                                
            .map_err(|e| "input B error")?;                                                                                                                                   
        let b : i32 = input.trim_right().parse()                                                                                                                              
            .map_err(|e| "parse B error.")?;                                                                                                                                  
                                                                                                                                                                              
        Ok(format!("{}", a + b))                                                                                                                                              
    }                                                                                                                                                                         
}

fn main() {
    println!("{}", programming_education().unwrap());
}