#include using namespace std; char s[3005][3005]; int dist[3005][3005]; int main(){ int n,m; scanf("%d%d",&n,&m); for(int i=1;i<=n;++i)scanf("%s",s[i]+1); memset(dist,63,sizeof(dist)); queue>q; for(int i=0;i<=n+1;++i)for(int j=0;j<=m+1;++j){ if(i==0||i==n+1||j==0||j==m+1){ dist[i][j]=0;q.emplace(i,j); }else if(s[i][j]!='#'){ dist[i][j]=0;q.emplace(i,j); } } int ans=0; while(q.size()){ auto au=q.front();q.pop(); int x=au.first,y=au.second; ans=max(ans,dist[x][y]); for(int i=-1;i<=1;++i)for(int j=-1;j<=1;++j){ int dx=x+i,dy=y+j; if(dx<1||dx>n||dy<1||dy>m)continue; if(dist[dx][dy]>dist[x][y]+1){ dist[dx][dy]=dist[x][y]+1; q.emplace(dx,dy); } } } printf("%d\n",ans); return 0; }