#include <bits/stdc++.h>
using namespace std;
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, -1, 0, 1};
const int N = 505;
int n, m;
char mp[N * 2][N * 2];
inline void Dfs(int x, int y, int de, int dis[N][N], int fr[N][N]) {
    if (dis[x][y]) return;
    dis[x][y] = de;
    int tx = x * 2, ty = y * 2;
    for (int d = 0; d < 4; ++d) if (mp[tx + dx[d]][ty + dy[d]] == '.' && !dis[x + dx[d]][y + dy[d]]) {
        fr[x + dx[d]][y + dy[d]] = d ^ 2;
        Dfs(x + dx[d], y + dy[d], de + 1, dis, fr);
    }
}
int bel[N][N];
int d0[N][N], d1[N][N];
int fr0[N][N], fr1[N][N];
multiset<int> st;
inline void Paint(int x, int y) {
    if (bel[x][y]) return;
    // printf("Paint %d %d\n", x, y);
    bel[x][y] = 1;
    int tx = x * 2, ty = y * 2;
    for (int d = 0; d < 4; ++d) {
        int nx = x + dx[d], ny = y + dy[d];
        if (nx > n || nx == 0 || ny > m || ny == 0) continue;
        if (bel[nx][ny] == 1) {
            st.erase(st.find(d0[x][y] + d1[nx][ny]));
        } else {
            st.insert(d1[x][y] + d0[nx][ny]);
        }
    }
    for (int d = 0; d < 4; ++d) if (mp[tx + dx[d]][ty + dy[d]] == '.') {
        Paint(x + dx[d], y + dy[d]);
    }
}
int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= 2 * n + 1; ++i) scanf("%s", mp[i] + 1);
    Dfs(1, 1, 1, d0, fr0);
    Dfs(n, m, 1, d1, fr1);
    int ans = d0[n][m];
    for (int i = n, j = m; i != 1 || j != 1; ) {
        int d = fr0[i][j];
        int ti = i * 2, tj = j * 2;
        mp[ti + dx[d]][tj + dy[d]] = '*';
        // printf("del %d %d\n", ti + dx[d], tj + dy[d]);
        Paint(i, j);
        // printf("%d %d  %d\n", i, j, *--st.end());
        ans = max(ans, *--st.end());
        i += dx[d];
        j += dy[d];
    }
    printf("%d\n", ans);
    return 0;
}