use proconio::input;
use proconio::marker::Chars;

fn main () {
    input! {
        h: usize,
        _: usize,
        s: [Chars; h],
        t: [Chars; h],
    }
    let s_rev = s.iter()
        .rev()
        .map(|c| {
            c.iter().rev().cloned().collect::<Vec<_>>()
        })
        .collect::<Vec<_>>();
    let t = t.iter()
        .map(|v| {
            v.iter().map(|&c| if c == '.' {'#'} else {'.'}).collect::<Vec<_>>()
        })
        .collect::<Vec<_>>();
    match (s, s_rev, t) {
        (s, s_rev, t) 
        if (s == t) & (s_rev == t) => {
            println!("{}", 2.641632560655154);
        },
        (s, _, t)
        if s == t => {
            println!("{}", 3.531740190461733);
        },
        (_, s_rev, t)
        if s_rev == t => {
            println!("{}", 3.128936827211877);
        },
        (_, _, _) => {
            println!("{}", -1);
        },
    }
}