#include<bits/stdc++.h>
using namespace std;
char a[1205][1205];
int n, m;
int idTrans(int x, int y){
    return x * m + y;
}
vector<int> graph[250005];
void add_edge(int x, int y){
    graph[x].push_back(y);
    graph[y].push_back(x);
}
bool vis[250005];
int from_s[250005], from_t[250005], id[250005];
vector<int> stk;
bool haveFoundPath = 0;
int s, t;
void dfsFromS(int x, int fa = -1, int d = 1){
    if(!haveFoundPath){
        stk.push_back(x);
    }
    from_s[x] = d;
    if(x == t){
        haveFoundPath = 1;
    }
    for(auto i : graph[x]){
        if(i == fa)
            continue;
        dfsFromS(i, x, d + 1);
    }
    if(!haveFoundPath){
        stk.pop_back();
    }
}
void dfsFromT(int x, int fa = -1, int d = 1){
    from_t[x] = d;
    for(auto i : graph[x]){
        if(i == fa)
            continue;
        dfsFromT(i, x, d + 1);
    }
}
void dfsPush(int x){
    for(auto i : graph[x]){
        if(!id[i]){
            id[i] = id[x];
            dfsPush(i);
        }
    }
}
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> m;
    s = 0;
    t = n * m - 1;
    vector<pair<int, int> > canadd;
    for(int i = 0; i < 2 * n + 1; i++){
        for(int j = 0; j < 2 * m + 1; j++){
            cin >> a[i][j];
            if(i > 0 && i < 2 * n && !(i & 1) && (j & 1)){
                if(a[i][j] == '.')
                    add_edge(idTrans(i / 2 - 1, j / 2), idTrans(i / 2, j / 2));
                else
                    canadd.push_back({idTrans(i / 2 - 1, j / 2), idTrans(i / 2, j / 2)});
            }
            if(j > 0 && j < 2 * m && !(j & 1) && (i & 1)){
                if(a[i][j] == '.')
                    add_edge(idTrans(i / 2, j / 2 - 1), idTrans(i / 2, j / 2));
                else
                    canadd.push_back({idTrans(i / 2, j / 2 - 1), idTrans(i / 2, j / 2)});
            }
        }
    }
    dfsFromS(s);
    dfsFromT(t);
    for(int i = 0; i < stk.size(); i++){
        id[stk[i]] = i + 1;
    }
    for(auto i : stk){
        dfsPush(i);
    }
    int ans = stk.size();
    for(auto &i : canadd){
        if(id[i.first] != id[i.second]){
            ans = max(ans, min(from_s[i.first] + from_t[i.second], from_t[i.first] + from_s[i.second]));
        }
    }
    cout << ans << '\n';
}