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: Accepted)

#![allow(bare_trait_objects)]
#![allow(unused_imports)]
#![allow(dead_code)]

use std::fmt::Debug;
use std::io::BufRead;
use std::io::Stdin;
use std::io::StdinLock;
use std::str::FromStr;

pub struct Scanner<'a> {
    buf_read: Box<BufRead + 'a>,
    tokens: Vec<String>,
}

impl<'a> Scanner<'a> {
    pub fn new(buf_read: StdinLock<'a>) -> Self {
        Scanner {
            buf_read: Box::new(buf_read),
            tokens: Vec::new(),
        }
    }

    // pub fn from_stdin() -> Self {
    //     let stdin = Box::leak(Box::new(std::io::stdin()));
    //     Self {
    //         buf_read: Box::new(stdin.lock()),
    //         tokens: Vec::new(),
    //     }
    // }

    pub fn next(&mut self) -> String {
        while self.tokens.is_empty() {
            let mut s = String::new();
            if self.buf_read.read_line(&mut s).is_err() {
                panic!()
            }
            self.tokens = s
                .split_whitespace()
                .filter(|s| !s.is_empty())
                .rev()
                .map(str::to_string)
                .collect();
        }
        self.tokens.pop().unwrap()
    }

    pub fn next_g<T: FromStr>(&mut self) -> T
    where
        T::Err: Debug,
    {
        self.next().parse().unwrap()
    }

    pub fn next_vec_g<T: FromStr>(&mut self, n: usize) -> Vec<T>
    where
        T::Err: Debug,
    {
        (0..n).map(|_| self.next_g()).collect()
    }

    pub fn usize(&mut self) -> usize {
        self.next_g()
    }

    pub fn i64(&mut self) -> i64 {
        self.next_g()
    }

    pub fn vec_i64(&mut self, n: usize) -> Vec<i64> {
        self.next_vec_g(n)
    }

    pub fn vec_usize(&mut self, n: usize) -> Vec<usize> {
        self.next_vec_g(n)
    }

    pub fn chars(&mut self) -> Vec<char> {
        self.next().chars().collect()
    }
}

fn main() {
    let stdin = std::io::stdin();
    let mut sc = Scanner::new(stdin.lock());

    let n = sc.usize() - 1;
    let cs: Vec<_> = sc.chars().iter().map(|c| *c as i32 - '1' as i32).collect();

    let c = if cs.iter().all(|v| *v != 1) { 2 } else { 1 };

    let mut div2 = vec![0; n + 1];
    for i in 1..div2.len() {
        div2[i] = div2[i - 1];
        let mut j = i;
        while j % 2 == 0 {
            div2[i] += 1;
            j /= 2;
        }
    }

    let mut ans = 0;
    for i in 0..n + 1 {
        let cnt2 = div2[n] - div2[n - i] - div2[i];
        if cnt2 == 0 && cs[i] == c {
            ans ^= c;
        }
    }

    println!("{}", ans);
}