Problem:
Score : 700 points

Problem Statement

Given is a sequence of N digits a_1a_2\ldots a_N, where each element is 1, 2, or 3.
Let x_{i,j} defined as follows:

x_{1,j} := a_j \quad (1 \leq j \leq N)

x_{i,j} := | x_{i-1,j} - x_{i-1,j+1} | \quad (2 \leq i \leq N and 1 \leq j \leq N+1-i)

Find x_{N,1}.

Constraints

2 \leq N \leq 10^6

a_i = 1,2,3 (1 \leq i \leq N)

Input

Input is given from Standard Input in the following format:

N
a_1a_2\ldotsa_N

Output

Print x_{N,1}.

Sample Input 1

4
1231

Sample Output 1

1

x_{1,1},x_{1,2},x_{1,3},x_{1,4} are respectively 1,2,3,1.

x_{2,1},x_{2,2},x_{2,3} are respectively |1-2| = 1,|2-3| = 1,|3-1| = 2.

x_{3,1},x_{3,2} are respectively |1-1| = 0,|1-2| = 1.

Finally, x_{4,1} = |0-1| = 1, so the answer is 1.

Sample Input 2

10
2311312312

Sample Output 2

0

Solution in Rust (1.15.1) (judge verdict: Wrong Answer)

#![allow(unused_imports)]
#![allow(non_snake_case)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let n = read::<usize>();
    let a = read::<String>()
        .chars()
        .map(|x| x.to_digit(10).unwrap() as i64)
        .collect::<Vec<_>>();

    let mut b = vec![];
    for i in 0..n - 1 {
        b.push((a[i] - a[i + 1]).abs());
    }
    if n == 2 {
        println!("{}", b[0]);
        return;
    }
    let zero_count = b.iter().filter(|&&x| x == 0).count();
    if zero_count == b.len() - 1 && (b[0] > 0 || b[b.len() - 1] > 0) {
        println!("{}", b.iter().max().unwrap());
        return;
    }
    let b = b.into_iter().map(|x| x % 2).collect::<Vec<_>>();
    // debug!(b);

    let mut ans = b[0];
    for i in 1..b.len() {
        let all = 1 << i;
        let half = all / 2;

        if b[i] == 1 && ((b.len() - i - 1) % all) < half {
            // debug!(all, half, (b.len() - i - 1) % all);
            ans ^= 1;
        }
    }
    println!("{}", ans);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}