fn lcp<T, I>(a: I, b: I) -> usize
where
    T: Eq,
    I: Iterator<Item = T>
{
    a.zip(b).take_while(|p| p.0 == p.1).count()
}


fn run() {
    input! {
        n: usize,
        m: usize,
        s: [bytes; n],
    }
    let mut ans = vec![];
    let x = lcp(s[0].iter(), s[1].iter());
    for &(a, c) in [(&s[0], s[1][x]), (&s[1], s[0][x])].iter() {
        let mut a = a.iter().cloned().collect::<Vec<_>>();
        a.insert(x, c);
        if s.iter().all(|s| {
            let x = lcp(s.iter(), a.iter());
            let y = lcp(s.iter().rev(), a.iter().rev());
            x + y >= m
        }) {
            ans.push(a);
        }
    }
    ans.sort();
    ans.dedup();
    println!("{}", ans.len());
}

fn main() {
    run();
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------