#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; using ull = unsigned long long; using ll = long long; using lli = long long int; using ld = long double; using pa = pair; using ppa = pair; #define SORT(v, n) sort(v, v+n); #define ALL(v) v.begin(),v.end() #define VSORT(v) sort(ALL(v)) #define GRESORT(v) sort(ALL(v),greater()) #define REVERSE(v) reverse(ALL(v)) #define overlap(v) v.erase(unique(ALL(v)),v.end()) #define debug(x) cout << #x << ": " << x << endl #define FOR(i,a,b) for(int i = (a); i < (b); i++) #define rep(i,n) FOR(i,0,n) #define RFOR(i,a,b) for(int i = (b-1); i >= a; i--) #define rrep(i,n) RFOR(i,0,n) #define INF INT_MAX #define mins(a,b) a = min(a,b) #define maxs(a,b) a = max(a,b) //4近傍 //int dy[]={0, 1, 0, -1}; //int dx[]={1, 0, -1, 0}; //8近傍 int dy[]={0,0,1,-1,1,1,-1,-1}; int dx[]={1,-1,0,0,1,-1,1,-1}; ll MOD = 1000000007; int h,w; bool check(int x,int y){ return y < 0 || x < 0 || y >= h || x >= w; } void solve() { cin >> h >> w; vector s(h); rep(i,h) cin >> s[i]; vector> d(h,vector(w,INF)); queue q; rep(i,w) if(s[0][i] == '#'){ d[0][i] = 1; q.push(pa(i,0)); } rep(i,w) if(s[h-1][i] == '#'){ d[h-1][i] = 1; q.push(pa(i,h-1)); } rep(i,h) if(s[i][0] == '#'){ d[i][0] = 1; q.push(pa(0,i)); } rep(i,h) if(s[i][w-1] == '#'){ d[i][w-1] = 1; q.push(pa(w-1,i)); } rep(i,h){ rep(j,w){ if(s[i][j] == '.'){ rep(k,8){ int yy = i + dy[k]; int xx = j + dx[k]; if(check(xx,yy) || d[yy][xx] != INF || s[yy][xx] == '.') continue; d[yy][xx] = 1; q.push(pa(xx,yy)); } } } } int ans = 0; while(!q.empty()){ pa p = q.front(); q.pop(); int x = p.first, y = p.second; maxs(ans,d[y][x]); rep(i,8){ int yy = y + dy[i]; int xx = x + dx[i]; if(check(xx,yy) || d[yy][xx] != INF || s[yy][xx] == '.') continue; d[yy][xx] = d[y][x] + 1; q.push(pa(xx,yy)); } } cout << ans << endl; } int main(){ std::ios::sync_with_stdio(false); std::cin.tie(0); solve(); return 0; }