// -*- coding:utf-8-unix -*-
// #![feature(map_first_last)]
#![allow(dead_code)]
#![allow(unused_imports)]
#![allow(unused_macros)]
// use core::num;
use std::cmp::*;
use std::fmt::*;
use std::hash::*;
use std::iter::FromIterator;
use std::*;
use std::{cmp, collections, fmt, io, iter, ops, str};
const INF: i64 = 1223372036854775807;
const UINF: usize = INF as usize;
const LINF: i64 = 2147483647;
const INF128: i128 = 1223372036854775807000000000000;
const MOD1: i64 = 1000000007;
const MOD9: i64 = 998244353;
const MOD: i64 = MOD9;
// const MOD: i64 = MOD2;
const UMOD: usize = MOD as usize;
const M_PI: f64 = 3.14159265358979323846;

// use proconio::input;
// const MOD: i64 = INF;

use cmp::Ordering::*;
use std::collections::*;

use std::io::stdin;
use std::io::stdout;
use std::io::Write;

macro_rules! p {
    ($x:expr) => {
        //if expr
        println!("{}", $x);
    };
}

macro_rules! vp {
    // vector print separate with space
    ($x:expr) => {
        println!(
            "{}",
            $x.iter()
                .map(|x| x.to_string())
                .collect::<Vec<_>>()
                .join(" ")
        );
    };
}

macro_rules! d {
    ($x:expr) => {
        eprintln!("{:?}", $x);
    };
}
macro_rules! yn {
    ($val:expr) => {
        if $val {
            println!("Yes");
        } else {
            println!("No");
        }
    };
}

macro_rules! map{
    // declear btreemap
    ($($key:expr => $val:expr),*) => {
        {
            let mut map = ::std::collections::BTreeMap::new();
            $(
                map.insert($key, $val);
            )*
            map
        }
    };
}

macro_rules! set{
    // declear btreemap
    ($($key:expr),*) => {
        {
            let mut set = ::std::collections::BTreeSet::new();
            $(
                set.insert($key);
            )*
            set
        }
    };
}

//input output
#[allow(dead_code)]
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

#[allow(dead_code)]
fn read_mat<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

#[allow(dead_code)]
fn readii() -> (i64, i64) {
    let mut vec: Vec<i64> = read_vec();
    (vec[0], vec[1])
}

#[allow(dead_code)]
fn readiii() -> (i64, i64, i64) {
    let mut vec: Vec<i64> = read_vec();
    (vec[0], vec[1], vec[2])
}
#[allow(dead_code)]
fn readuu() -> (usize, usize) {
    let mut vec: Vec<usize> = read_vec();
    (vec[0], vec[1])
}

#[allow(dead_code)]
fn readff() -> (f64, f64) {
    let mut vec: Vec<f64> = read_vec();
    (vec[0], vec[1])
}

fn readcc() -> (char, char) {
    let mut vec: Vec<char> = read_vec();
    (vec[0], vec[1])
}

fn readuuu() -> (usize, usize, usize) {
    let mut vec: Vec<usize> = read_vec();
    (vec[0], vec[1], vec[2])
}
#[allow(dead_code)]
fn readiiii() -> (i64, i64, i64, i64) {
    let mut vec: Vec<i64> = read_vec();
    (vec[0], vec[1], vec[2], vec[3])
}

#[allow(dead_code)]
fn readuuuu() -> (usize, usize, usize, usize) {
    let mut vec: Vec<usize> = read_vec();
    (vec[0], vec[1], vec[2], vec[3])
}

use std::io::BufRead;

fn rotate_180(s: &Vec<Vec<char>>) -> Vec<Vec<char>> {
    let h = s.len();
    let w = s[0].len();
    let mut rotated = vec![vec!['.'; w]; h];
    for i in 0..h {
        for j in 0..w {
            rotated[h - i - 1][w - j - 1] = s[i][j];
        }
    }
    rotated
}

fn compare(s: &Vec<Vec<char>>, t: &Vec<Vec<char>>) -> bool {
    let h = s.len();
    let w = s[0].len();
    for i in 0..h {
        for j in 0..w {
            if s[i][j] == t[i][j] {
                return false;
            }
        }
    }
    true
}

fn main() {
    let stdin = io::stdin();
    let mut lines = stdin.lock().lines();

    let first_line = lines.next().unwrap().unwrap();
    let dimensions: Vec<usize> = first_line
        .split_whitespace()
        .map(|x| x.parse().unwrap())
        .collect();
    let h = dimensions[0];
    let w = dimensions[1];

    let mut s = Vec::new();
    let mut t = Vec::new();

    for _ in 0..h {
        let line = lines
            .next()
            .unwrap()
            .unwrap()
            .chars()
            .collect::<Vec<char>>();
        s.push(line);
    }

    for _ in 0..h {
        let line = lines
            .next()
            .unwrap()
            .unwrap()
            .chars()
            .collect::<Vec<char>>();
        t.push(line);
    }
    d!(s);
    d!(t);

    // 回転したSを作成
    let rotated_s = rotate_180(&s);
    let success1 = compare(&s, &t);
    let succsess2 = compare(&rotated_s, &t);
    if success1 {
        //0 + (1-1/(2^2) +(1- 1/(2^4)))
        let mut ans = 0.0;
        let mut prob = 1.0;
        for i in 0..1000 {
            let mut success = 1.0 - 1.0 / (2.0 as f64).powi(i);
            if i % 2 == 0 {
                ans += (i as f64 + 1.0) * prob * success;
                prob *= 1.0 - success;
            }
        }
        // p!(ans);
    } else if succsess2 {
        //0 + (1-1/(2^2) +(1- 1/(2^4)))
        let mut ans = 0.0;
        let mut prob = 1.0;
        for i in 0..1000 {
            let mut success = 1.0 - 1.0 / (2.0 as f64).powi(i);
            if i % 2 == 1 {
                ans += (i as f64 + 1.0) * prob * success;
                prob *= 1.0 - success;
            }
        }
        p!(ans);
    } else {
        p!(-1);
    }
}