#[allow(unused_imports)]
use std::cmp::{Ordering};

#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};

#[allow(unused_imports)]
use std::io::{stdin, stdout, BufWriter, Write};

#[allow(unused_imports)]
use std::iter::FromIterator;

#[allow(unused_macros)]
macro_rules! min {
    ($x: expr) => ($x);
    ($x: expr, $($z: expr),+) => {{
        std::cmp::min($x, min!($($z),*))
    }}
}

#[allow(unused_macros)]
macro_rules! max {
    ($x: expr) => ($x);
    ($x: expr, $($z: expr),+) => {{
        std::cmp::max($x, max!($($z),*))
    }}
}

#[allow(unused_macros)]
macro_rules! get { 
    ([$t: ty]) => { 
        { 
            let mut line = String::new(); 
            stdin().read_line(&mut line).unwrap(); 
            line.split_whitespace().map(|t|t.parse::<$t>().unwrap()).collect::<Vec<_>>()
        }
    };
    ([$t: ty];$n: expr) => {
        (0..$n).map(|_|get!([$t])).collect::<Vec<_>>()
    };
    ($t: ty) => {
        {
            let mut line = String::new();
            stdin().read_line(&mut line).unwrap();
            line.trim().parse::<$t>().unwrap()
        }
    };
    ($($t: ty),*) => {
        { 
            let mut line = String::new();
            stdin().read_line(&mut line).unwrap();
            let mut iter = line.split_whitespace();
            ($(iter.next().unwrap().parse::<$t>().unwrap(),)*)
        }
    };
    ($t: ty; $n: expr) => {
        (0..$n).map(|_|get!($t)).collect::<Vec<_>>()
    };
    ($($t: ty),*; $n: expr) => {
        (0..$n).map(|_|get!($($t),*)).collect::<Vec<_>>()
    };
}

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

const BIG_STACK_SIZE: bool = true;

#[allow(dead_code)]
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}

fn lower_bound<F>(l: usize, r: usize, criterion: F) -> usize
where
    F: Fn(usize) -> bool,
{
    let mut l = l;
    let mut r = r;
    while r - l > 1 {
        let mid = l + (r - l) / 2;
        if criterion(mid) {
            r = mid;
        } else {
            l = mid;
        }
    }
    if criterion(l) {
        l
    } else {
        r
    }
}

fn solve() {
    let n = get!(usize);
    let s = get!(String).chars().collect::<Vec<_>>();

    let mut first = vec![Vec::new(); n+1];
    for i in 0..1usize<<n {
        let mut red = String::new();
        let mut blue = String::new();
        for j in 0..n {
            if (i>>j)%2 == 1 {
                red.push(s[j]);
            } else {
                blue.push(s[j]);
            }
        }
        let blue = blue.chars().rev().collect::<String>();
        first[red.len()].push((red, blue));
    }

    for i in 0..n+1 {
        first[i].sort();
    }
    let mut count = 0usize;
    for i in 0..1usize<<n {
        let mut red = String::new();
        let mut blue = String::new();
        for j in 0..n {
            if (i>>j)%2 == 1 {
                red.push(s[j+n]);
            } else {
                blue.push(s[j+n]);
            }
        }
        let blue = blue.chars().rev().collect::<String>();

        let blen = blue.len();
        let bcrit1 = |index: usize| {
            blue <= first[blen][index].0
        };
        let bcrit2 = |index: usize| {
            blue < first[blen][index].0
        };
        let bindex1 = lower_bound(0, first[blen].len(), bcrit1);
        let bindex2 = lower_bound(0, first[blen].len(), bcrit2);

        if bindex1 == bindex2 {
            continue;
        }
        let rcrit1 = |index: usize| {
            red <= first[blen][index].1
        };
        let rcrit2 = |index: usize| {
            red < first[blen][index].1
        };
        let rindex1 = lower_bound(bindex1, bindex2, rcrit1);
        let rindex2 = lower_bound(bindex1, bindex2, rcrit2);
        let val = rindex2-rindex1;
        count += val;
    }
    println!("{}", count);
}


Measured memory_bytes: 38268