use proconio::{input, marker::Chars};

fn main() {
    input! {
        h:usize,
        w:usize,
        s:[Chars;h],
        t:[Chars;h],
    }

    let mut s_rev = vec![vec!['.'; w]; h];
    for i in 0..h {
        for j in 0..w {
            s_rev[i][w - j - 1] = s[h - i - 1][j];
        }
    }

    let f1 = (0..h).all(|i| (0..w).all(|j| s[i][j] != t[i][j]));
    let f2 = (0..h).all(|i| (0..w).all(|j| s_rev[i][j] != t[i][j]));

    let ans = if f1 && f2 {
        2.641632560655154
    } else if f1 {
        3.531740190461733
    } else if f2 {
        3.128936827211877
    } else {
        -1.0
    };

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