#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
const int N = 505;
char a[2 * N][2 * N];
int id[N][N];
int vst[N * N], dep[N * N], fa[N * N], color[N * N];
vector<int> e[N * N];
pair<int, int> g[N * N];
int main() {
	int n, m;
	scanf("%d%d", &n, &m);
	for(int i = 0; i < 2 * n + 1; i++) {
		scanf("%s", a[i]);
	}
	for(int i = 0; i < n; i++) {
		for(int j = 0; j < m; j++) {
			id[i][j] = i * m + j;
		}
	}
	int ng = 0;
	for(int i = 0; i < n; i++) {
		for(int j = 0; j < m; j++) {
			if(j < m - 1) {
				if(a[i * 2 + 1][j * 2 + 2] == '.') {
					e[id[i][j]].pb(id[i][j + 1]);
				}else {
					g[ng++] = pair<int, int>{id[i][j], id[i][j + 1]};
				}
			}
			if(i < n - 1) {
				if(a[i * 2 + 2][j * 2 + 1] == '.') {
					e[id[i][j]].pb(id[i + 1][j]);
				}else {
					g[ng++] = pair<int, int>{id[i][j], id[i + 1][j]};
				}
			}
		}
	}
	vector<int> q;
	q.pb(0);
	dep[0] = 0;
	vst[0] = 1;
	fa[0] = 0;
	for(int op = 0; op < (int)q.size(); op++) {
		int v = q[op];
		for(int y : e[v]) {
			if(!vst[y]) {
				vst[y] = true;
				dep[y] = dep[v] + 1;
				fa[y] = v;
				q.pb(y);
			}
		}
	}
	int x = n * m - 1;
	fill(color, color + n * m, -1);
	while(x != 0) {
		color[x] = x;
		x = fa[x];
	}
	color[0] = 0;
	fill(vst, vst + n * m, 0);
	q.clear();
	q.pb(0);
	vst[0] = 1;
	for(int op = 0; op < (int)q.size(); op++) {
		int v = q[op];
		for(int y : e[v]) {
			if(!vst[y]) {
				vst[y] = true;
				if(color[y] == -1) {
					color[y] = color[v];
				}
				q.pb(y);
			}
		}
	}
	int ans = dep[n * m - 1];
	for(int i = 0; i < ng; i++) {
		int x = g[i].fi;
		int y = g[i].se;
		int fx = color[x];
		int fy = color[y];
		if(fx == fy) continue;
		int len = dep[n * m - 1] + 1 + (dep[x] - dep[fx]) + (dep[y] - dep[fy]) - abs(dep[fx] - dep[fy]);
		ans = max(ans, len);
	}
	printf("%d\n", ans + 1);
}