#include <bits/stdc++.h>
#define ll long long
#define int ll
#define mp make_pair
#define fi first
#define se second
#define pb push_back
#define vi vector<int>
#define pi pair<int, int>
#define vpii vector<pi>
#define il inline
#define ri register
#define all(a) a.begin(), a.end()
#define fr(a) freopen(a, "r", stdin)
#define fo(a) freopen(a, "w", stdout);
#define mod 998244353
#define debug puts("------------------------")
#define lowbit(x) (x&-x)
#define ls(x) x << 1
#define rs(x) x << 1 | 1
template<typename T> bool chkmin(T &a, T b){return (b < a) ? a = b, 1 : 0;}
template<typename T> bool chkmax(T &a, T b){return (b > a) ? a = b, 1 : 0;}
ll ksm(ll a, ll b) {if (b == 0) return 1; ll ns = ksm(a, b >> 1); ns = ns * ns % mod; if (b & 1) ns = ns * a % mod; return ns;}
void Read(int &a) {a=0;int c=getchar(),b=1; while(c>'9'||c<'0') {if(c=='-')b=-1;c=getchar();} while(c>='0'&&c<='9') a=(a<<3)+(a<<1)+c-48,c=getchar();a*=b; }
int  read() {int a=0,c=getchar(),b=1; while(c>'9'||c<'0') {if(c=='-')b=-1;c=getchar();} while(c>='0'&&c<='9') a=(a<<3)+(a<<1)+c-48,c=getchar();return a*=b; }
void write(int x) {if(x>9)write(x/10);putchar('0'+x%10);}
void W(int x) {if(x<0){putchar('-'),x=-x;}write(x);}
#define LOCAL
using namespace std;
const int maxn = 1005;
/**/
int n, m;
char s[maxn][maxn];
int id[maxn][maxn], num;
pi rid[maxn * maxn];
vi g[maxn * maxn];
int dis[2][maxn * maxn], st, ed;
int vis[maxn * maxn];
vi vec;
queue<int>q;
const int fx[] = {0, 0, 1, -1};
const int fy[] = {1, -1, 0, 0};
bool ok(int x, int y)
{
	return x >= 2 && y >= 2 && x <= 2 * n && y <= 2 * m;
}
/**/
void dfs(int u, int fa, int rt)
{
	dis[rt == 1][u] = dis[rt == 1][fa] + 1;
	for(auto v : g[u])
	{
		if(v == fa) continue;
		dfs(v, u, rt);
	}
}
void col(int u, int fa)
{
	vis[u] = 1;
	vec.pb(u);
	for(auto v : g[u])
	{
		if(v == fa || vis[v]) continue;
		if(dis[1][v] + dis[0][v] - 1 == dis[1][ed])
		{
			q.push(v);
			continue;
		}
		col(v, u);
	}
}
signed main()
{
	n = read(); m = read();
	for(int i = 1; i <= 2 * n + 1; i++)
	{
		scanf("%s", s[i] + 1);
	}
	for(int x = 2; x <= 2 * n; x += 2)
	{
		for(int y = 2; y <= 2 * m; y += 2)
		{
			id[x][y] = ++num;
			rid[num] = {x, y};
		}
	}
	// cout << num << "\n";
	for(int x = 2; x <= 2 * n; x += 2)
	{
		for(int y = 2; y <= 2 * m; y += 2)
		{
			for(int i = 0; i < 4; i++)
			{
				int dx = x + fx[i];
				int dy = y + fy[i];
				int x_ = dx + fx[i];
				int y_ = dy + fy[i];
				
				if(!ok(x_, y_)) continue;
				if(s[dx][dy] == '.')
				{
					int u = id[x][y], v = id[x_][y_];
					g[u].pb(v);
					// cout << u << " -> " << v << "\n";
				}
			}
		}
	}
	st = 1, ed = n * m;
	dfs(st, 0, st);
	dfs(ed, 0, ed);
	// for(int i = 1; i <= n * m; i++) cout << dis[1][i] << "\n";
	int ans = dis[1][n * m];
	// cout << "ans = " << ans << "\n";
	q.push(1);
	while(!q.empty())
	{
		int u = q.front(); q.pop(); vec.clear();
		col(u, 0);
		// puts("------");
		// cout << u << ": \n";
		// for(auto ii : vec) cout << ii << " "; puts("");
		for(auto ii : vec)
		{
			int x = rid[ii].fi, y = rid[ii].se;
			for(int i = 0; i < 4; i++)
			{
				int dx = x + fx[i], dy = y + fy[i];
				int x_ = dx + fx[i], y_ = dy + fy[i];
				if(!ok(x_, y_) || vis[id[x_][y_]]) continue;
				// cout << ii << " -> " << id[x_][y_] << "\n";
				// cout << dis[1][ii] << " + " << dis[n][id[x_][y_]] << "\n"; 
				ans = max(ans, dis[1][ii] + dis[0][id[x_][y_]]);
			}
		}
	}
	cout << ans << "\n";
	return 0;
}