#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

struct UnionFind {
	vector<int> data;
	void init(int n) { data.assign(n, -1); }
	bool unionSet(int x, int y) {
		x = root(x); y = root(y);
		if(x != y) {
			if(data[y] < data[x]) swap(x, y);
			data[x] += data[y]; data[y] = x;
		}
		return x != y;
	}
	bool findSet(int x, int y) { return root(x) == root(y); }
	int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
	int size(int x) { return -data[root(x)]; }
};

static const int dy[4] = {0,1,0,-1}, dx[4] = {1,0,-1,0};

int main() {
	int W, H;
	scanf("%d%d", &W, &H);
	char C[20][21];
	rep(i, H) scanf("%s", C[i]);
	UnionFind uf; uf.init(H * W);
	rep(i, H) rep(j, W) if(C[i][j] == '.') {
		rep(d, 4) {
			int yy = i + dy[d], xx = j + dx[d];
			if(yy<0||yy>=H||xx<0||xx>=W) continue;
			if(C[yy][xx] == '.')
				uf.unionSet(i * W + j, yy * W + xx);
		}
	}
	int ans = INF;
	rep(si, H) rep(sj, W) if(C[si][sj] == '.') {
		int s = si * W + sj;
		vpii q, nq;
		rep(i, H) rep(j, W) if(C[i][j] == '.' && uf.findSet(s, i * W + j)) {
			rep(d, 4) {
				int yy = i + dy[d], xx = j + dx[d];
				if(yy<0||yy>=H||xx<0||xx>=W) continue;
				if(C[yy][xx] == '#')
					nq.push_back(mp(yy, xx));
			}
		}
		int t = 0;
		bool vis[20][21] = {};
		while(!nq.empty()) {
			q.swap(nq);
			while(!q.empty()) {
				int i = q.back().first, j = q.back().second; q.pop_back();
				if(vis[i][j]) continue;
				vis[i][j] = true;
				rep(d, 4) {
					int yy = i + dy[d], xx = j + dx[d];
					if(yy<0||yy>=H||xx<0||xx>=W) continue;
					if(C[yy][xx] == '#') {
						nq.push_back(mp(yy, xx));
					}else if(!uf.findSet(s, yy * W + xx)) {
						amin(ans, t + 1);
					}
				}
			}
			++ t;
		}
	}
	printf("%d\n", ans);
	return 0;
}