Problem:
Score : 200 points

Problem Statement

You are given a string S consisting of lowercase English letters.
We will write down this string, starting a new line after every w letters. Print the string obtained by concatenating the letters at the beginnings of these lines from top to bottom.

Constraints

1 \leq w \leq |S| \leq 1000

S consists of lowercase English letters.

w is an integer.

Input

Input is given from Standard Input in the following format:

S
w

Output

Print the desired string in one line.

Sample Input 1

abcdefgh
3

Sample Output 1

adg

When we write down abcdefgh, starting a new line after every three letters, we get the following:

abc

def

gh

Concatenating the letters at the beginnings of these lines, we obtain adg.

Sample Input 2

lllll
1

Sample Output 2

lllll

Sample Input 3

souuundhound
2

Sample Output 3

suudon

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

fn main(){
  let s: String = read();
  let w: usize = read();

  let ans: String = s.chars().enumerate().filter_map(|(i, c)| if i % w == 0 {Some (c)} else {None}).collect();
  println!("{}", ans);
}

fn read<T>() -> T
  where T: std::str::FromStr,
        T::Err: std::fmt::Debug
{
  let mut buf = String::new();
  std::io::stdin().read_line(&mut buf).expect("failed to read");
  buf.trim().parse().unwrap()
}