#include <bits/stdc++.h>
#define rep(i, a, b) for (int i = a, I = b; i <= I; ++i)
#define per(i, a, b) for (int i = a, I = b; i >= I; --i)
using namespace std;

const int N = 250005;
int h, w, n, d1[N], d2[N], fa[N], X, Y, v1, vn, bel[N];
vector<int> e[N];

int ID(int i, int j) {
    return 1ll * (i - 1) * w + j;
}
void add_edge(int u, int v) {
    e[u].push_back(v);
    e[v].push_back(u);
}

void dfs(int u, int *dep) {
    for (auto v : e[u]) {
        if (v == fa[u]) continue;
        dep[v] = dep[u] + 1;
        fa[v] = u;
        dfs(v, dep);
    }
}
void dfs1(int u) {
    for (auto v : e[u]) {
        if (bel[v]) continue;
        bel[v] = bel[u];
        dfs1(v);
    }
}

int main() {
	ios::sync_with_stdio(0), cin.tie(0);

    cin >> h >> w, n = h * w;
    rep(i, 1, 2 * h + 1) {
        string s; cin >> s;
        if (i == 1 || i == 2 * h + 1) continue;
        if (i % 2 == 0) {
            rep(j, 1, w - 1) {
                if (s[2 * j] == '.') add_edge(ID(i / 2, j), ID(i / 2, j + 1));
            }
        } else {
            rep(j, 1, w) {
                if (s[2 * j - 1] == '.') add_edge(ID(i / 2, j), ID(i / 2 + 1, j));
            }
        }
    }

    dfs(n, d2);
    memset(fa, 0, sizeof fa);
    dfs(1, d1);

    int ans = d1[n], cnt = 0;
    for (int u = n; u; u = fa[u]) bel[u] = ++cnt;
    for (int u = n; u; u = fa[u]) dfs1(u);

    const int dx[] = {0, 0, 1, -1}, dy[] = {1, -1, 0, 0};
    rep(i, 1, h) rep(j, 1, w) {
        int u = ID(i, j);
        rep(d, 0, 3) {
            int i1 = i + dx[d], j1 = j + dy[d];
            if (i1 < 1 || i1 > h || j1 < 1 || j1 > w) continue;
            int v = ID(i1, j1);
            if (bel[u] < bel[v]) ans = max(ans, d2[u] + d1[v] + 1);
        }
    }

    cout << ans + 1 << "\n";

	return 0;
}