#include <bits/stdc++.h>
using namespace std;
string a[1010];
vector<int> G[510*510];
int d[510*510];
bool vis[510*510];
int n, m, N;
void add(int u, int v) {
    G[u].push_back(v);
    G[v].push_back(u);
}
int st[510*510], tot;
int ban[510*510], pp[510*510], len;
int b[510*510], ff[510*510], pos[510*510];
int mxdep;
#define P(x, y) ((x - 1) * m + y)
void dfs(int x, int fa) {
    st[++ tot] = x;
    if(x == P(n, m)) {
        len = tot;
        for(int i = 1; i <= tot; ++ i) {
            pp[i] = st[i];
            ban[pp[i]] = 1;
        }    
    }
    for(auto v : G[x]) {
        if(v == fa) continue;
        dfs(v, x);
    }
    -- tot;
}
void dfs(int x, int fa, int dep, int anc) {
    // mxdep = max(mxdep, dep);
    d[x] = dep; ff[x] = anc;
    for(auto v : G[x]) {
        if(v == fa) continue;
        if(ban[v]) continue;
        dfs(v, x, dep + 1, anc);
    }
}
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> m;
    N = n * m;
    for(int i = 1; i <= 2 * n + 1; ++ i) {
        cin >> a[i];
        a[i] = '0' + a[i];
    }
    for(int i = 1; i < n; ++ i) {
        for(int j = 1; j <= m; ++ j) {
            if(a[2 * i + 1][2 * j] == '.') {
                add(P(i, j), P(i + 1, j));
            }
        }
    }
    for(int i = 1; i <= n; ++ i) {
        for(int j = 1; j < m; ++ j) {
            if(a[2 * i][2 * j + 1] == '.') {
                add(P(i, j), P(i, j + 1));
            }
        }
    }
    dfs(P(1, 1), 0);
    for(int i = 1; i <= len; ++ i) {
        dfs(pp[i], 0, 1, pp[i]);
        pos[pp[i]] = i;
    }
    int Ans = len;
    for(int i = 1; i < n; ++ i) {
        for(int j = 1; j <= m; ++ j) {
            if(a[2 * i + 1][2 * j] != '.') {
                int u = P(i, j), v = P(i + 1, j);
                if(pos[ff[u]] > pos[ff[v]]) swap(u, v);
                int l = pos[ff[u]], r = pos[ff[v]];
                if(l == r) continue;
                // cerr << i << " " << j << " to " << i + 1 << " " << j << " res   " << len - (r - l + 1) + d[u] + d[v] << " " << d[u] << " " << d[v] << endl;
                Ans = max(Ans, len - (r - l + 1) + d[u] + d[v]);
            }
        }
    }
    for(int i = 1; i <= n; ++ i) {
        for(int j = 1; j < m; ++ j) {
            if(a[2 * i][2 * j + 1] != '.') {
                int u = P(i, j), v = P(i, j + 1);
                if(pos[ff[u]] > pos[ff[v]]) swap(u, v);
                int l = pos[ff[u]], r = pos[ff[v]];
                if(l == r) continue;
                // cerr << i << " " << j << " to " << i << " " << j + 1 << " res   " << len - (r - l + 1) + d[u] + d[v] << " " << d[u] << " " << d[v] << endl;
                Ans = max(Ans, len - (r - l + 1) + d[u] + d[v]);
            }
        }
    }
    // for(int i = 1; i <= N; ++ i) {
    //     cerr << d[i] << endl;
    // }
    cout << Ans << endl;
}