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)

///////////////////////////////////////////// Template /////////////////////////////////////////////
#![allow(non_snake_case, unused)]
use std::collections::*;

//////////////////// missing functions in 1.15.1 ////////////////////
macro_rules! eprint {
	($($t:tt)*) => { {
		use ::std::io::Write;
		let _ = write!(::std::io::stderr(), $($t)*);
	} };
}
macro_rules! eprintln {
	($($t:tt)*) => { {
		use ::std::io::Write;
		let _ = writeln!(::std::io::stderr(), $($t)*);
	} };
}

//////////////////// useful functions ////////////////////
pub trait SetMin {
	fn setmin(&mut self, v: Self) -> bool;
}
impl<T> SetMin for T where T: PartialOrd {
	fn setmin(&mut self, v: T) -> bool {
		*self > v && { *self = v; true }
	}
}
pub trait SetMax {
	fn setmax(&mut self, v: Self) -> bool;
}
impl<T> SetMax for T where T: PartialOrd {
	fn setmax(&mut self, v: T) -> bool {
		*self < v && { *self = v; true }
	}
}

macro_rules! debug {
	($($v: expr),*) => {
		$(eprint!("{} = {:?} ", stringify!($v), $v);)*
		eprintln!("@ {}:{}", file!(), line!());
	}
}

macro_rules! mat {
	($($e:expr),*) => { Vec::from(vec![$($e),*]) };
	($($e:expr,)*) => { Vec::from(vec![$($e),*]) };
	($e:expr; $d:expr) => { Vec::from(vec![$e; $d]) };
	($e:expr; $d:expr $(; $ds:expr)+) => { Vec::from(vec![mat![$e $(; $ds)*]; $d]) };
}

pub fn readln() -> String {
	let mut line = String::new();
	::std::io::stdin().read_line(&mut line).unwrap_or_else(|e| panic!("{}", e));
	line
}

macro_rules! read {
	($($t:tt),*; $n:expr) => {{
		let stdin = ::std::io::stdin();
		let ret = ::std::io::BufRead::lines(stdin.lock()).take($n).map(|line| {
			let line = line.unwrap();
			let mut it = line.split_whitespace();
			_read!(it; $($t),*)
		}).collect::<Vec<_>>();
		ret
	}};
	($($t:tt),*) => {{
		let line = readln();
		let mut it = line.split_whitespace();
		_read!(it; $($t),*)
	}};
}

macro_rules! _read {
	($it:ident; [char]) => {
		_read!($it; String).chars().collect::<Vec<_>>()
	};
	($it:ident; [u8]) => {
		Vec::from(_read!($it; String).into_bytes())
	};
	($it:ident; [$t:ty]) => {
		$it.map(|s| s.parse::<$t>().unwrap_or_else(|e| panic!("{}", e))).collect::<Vec<_>>()
	};
	($it:ident; $t:ty) => {
		$it.next().unwrap_or_else(|| panic!("input mismatch")).parse::<$t>().unwrap_or_else(|e| panic!("{}", e))
	};
	($it:ident; $($t:ty),+) => {
		($(_read!($it; $t)),*)
	};
}

pub fn main() {
	let _ = ::std::thread::Builder::new().name("run".to_string()).stack_size(32 * 1024 * 1024).spawn(run).unwrap().join();
}
////////////////////////////////////////////////////////////////////////////////////////////////////

fn run() {
	let s = read!([char]);
	let w = read!(usize);
	let mut i = 0;
	while i < s.len() {
		print!("{}", s[i]);
		i += w;
	}
	println!();
}