#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int h, w;
    cin >> h >> w;
    vector<string> s(h), t(h);
    rep(i,h) cin >> s[i];
    rep(i,h) cin >> t[i];
    bool a = true;
    rep(i,h)rep(j,w) if(s[i][j]==t[i][j]) a = false;
    bool b = true;
    rep(i,h)rep(j,w) if(s[i][j]==t[h-i-1][j]) b = false;
    if(!a && !b) {
        cout << -1 << endl;
        return 0;
    }
    lb ans = 0;
    lb pow = 1;
    lb sum = 1;
    dbg(a, b);
    for(int i=1;i<=100000;i++) {
        if(i%2==1 && a){
            sum *= pow;
            dbg((pow-1)/sum);
            ans += i * (pow-1) / (sum);
        }
        else if(i%2==0 && b) {
            sum *= pow;
            ans += i * (pow-1) / sum;
        }
        pow *= 2;
        dbg(pow,sum);
    }
    cout << fixed << setprecision(16) << ans << endl;
    return 0;
}