#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int h,w; cin >> h >> w;
    vector<string> str(2*h+1);
    for (int i = 0; i < str.size(); ++i) {
        cin >> str[i];
    }
    int n = h*w;
    vector<vector<int>> g(n);
    auto add_edge = [&](int i,int j,int d)->void{
        int x,y;
        if(d == 0){
            x = i*w+j, y = (i+1)*w+j;
        }
        else{
            x = i*w+j, y = i*w+j+1;
        }
        g[x].push_back(y);
        g[y].push_back(x);
    };

    vector<pair<int,int>> ta;
    auto adta = [&](int i,int j,int d)->void{
        int x,y;
        if(d == 0){
            x = i*w+j, y = (i+1)*w+j;
        }
        else{
            x = i*w+j, y = i*w+j+1;
        }
        ta.push_back({x,y});
    };
    int s = 0, t = n-1;
    for (int i = 0; i < h; ++i) {
        for (int j = 0; j < w; ++j) {
            if(i+1<h){
                if(str[2*i+2][j*2+1] == '.'){
                    add_edge(i,j,0);
                }
                else{
                    adta(i,j,0);
                }
            }
            if(j+1<w){
                if(str[i*2+1][j*2+2] == '.'){
                    add_edge(i,j,1);
                }
                else{
                    adta(i,j,1);
                }
            }
        }
    }
    vector<int> ds(n,-1),dt(n,-1);
    queue<int> q;
    ds[s] = 0, dt[t] = 0;
    q.push(s);
    while (q.size()){
        int v = q.front();
        q.pop();
        for(int u:g[v]){
            if(ds[u] == -1){
                ds[u] = ds[v]+1;
                q.push(u);
            }
        }
    }
    q.push(t);
    while (q.size()){
        int v = q.front();
        q.pop();
        for(int u:g[v]){
            if(dt[u] == -1){
                dt[u] = dt[v]+1;
                q.push(u);
            }
        }
    }
    vector<int> v;
    v.push_back(s);
    while (v.back() != t){
        for(int &to:g[v.back()]){
            if(dt[to]+1 == dt[v.back()]){
                int l = v.back();
                v.push_back(to);
                swap(to, g[l].back());
                g[l].pop_back();
                for(int &tt:g[to]){
                    if(tt == l){
                        swap(g[to].back(), tt);
                        g[to].pop_back(); break;
                    }
                }
                break;
            }
        }
    }
    int res = ds[t];
    vector<int> cls(n,-1);
    for (int i = 0; i < v.size(); ++i) {
        cls[v[i]] = i;
        q.push(v[i]);
        while(q.size()){
            int v = q.front();
            q.pop();
            for(int u:g[v]){
                if(cls[u] == -1){
                    cls[u] = cls[v];
                    q.push(u);
                }
            }
        }
    }
    for(auto p:ta){
        if(cls[p.first] == cls[p.second]) continue;
        res = max(res, min(ds[p.first]+dt[p.second]+1, dt[p.first]+ds[p.second]+1));
    }
    cout << res+1 << endl;
}