#include<bits/stdc++.h>
using namespace std;

struct vec2{
  int x;
  int y;
  vec2(int x,int y){
    this->x = x;
    this->y = y;
  }
};

short s[1000][1000];

int main(){

    int w,h;

    cin >> w >> h;

    short table[w][h];

    int dirx[8] = {-1,-1,-1,0,0,1,1,1},diry[8] = {-1,0,1,-1,1,-1,0,1};

    char c;

    for(int i=0;i<w;i++){
      for(int j=0;j<h;j++){
        cin >> c;
        if(c=='.'){
          table[i][j] = -1;
        }
        else{
          stringstream ss;
          ss << c;
          ss >> table[i][j];
        }
      }
    }

    int ans = 0,com=-1,rep=-3;

    queue<vec2> q1,q2;

    for(int i=1;i<w-1;i++){
      for(int j=1;j<h-1;j++){

        int count = 0;
        for(int k=0;k<8;k++){
          int di = i + dirx[k],dj = j + diry[k];
          if(table[di][dj] == -1){
            count++;
          }
        }

        s[i][j] = count;

        if(table[i][j] > 0 && count >= table[i][j]){
          vec2 tmpvec(i,j);
          q1.push(tmpvec);
          //table[i][j] = com;
        }


      }
    }

    /*for(int i=0;i<w;i++){
      for(int j=0;j<h;j++){
        cout << s[i][j] << " ";
      }
      cout << endl;
    }*/

  //  cout << endl;

    /*for(int i=1;i<w-1;i++){
      for(int j=1;j<h-1;j++){

          int count = 0;
          if(table[i+1][j] == com || table[i+1][j] == rep) count++;
          if(table[i+1][j-1] == com || table[i+1][j-1] == rep) count++;
          if(table[i+1][j+1] == com || table[i+1][j+1] == rep) count++;
          if(table[i][j-1] == com) count++;
          if(table[i][j+1] == com || table[i][j+1] == rep) count++;
          if(table[i-1][j] == com) count++;
          if(table[i-1][j+1] == com) count++;
          if(table[i-1][j-1] == com) count++;

          s[i][j] = count;

      }
    }*/

    /*for(int i=1;i<w-1;i++){
      for(int j=1;j<h-1;j++){

        if(table[i][j] == rep){
          table[i][j] = com;

        }
      }
    }*/

  /*  while(!q1.empty()){
      cout << q1.front().x << " " << q1.front().y << endl;
      q1.pop();
    }
    while(1){}*/

  /*  for(int i=0;i<w;i++){
      for(int j=0;j<h;j++){
        cout << table[i][j] << " ";
      }
      cout << endl;
    }
    cout << endl;*/

    if(q1.empty()) ans = -1;

    while(1){

      if(q1.empty()){
      /*  for(int i=0;i<w;i++){
          for(int j=0;j<h;j++){
            cout << table[i][j] << " ";
          }
          cout << endl;
        }
        cout << endl;*/
        ans++;
        if(q2.empty()){
          break;
        }
        else{
          while(!q2.empty()){
            //cout << ans << " " <<  q2.front().x << " " << q2.front().y << endl;
            q1.push(q2.front());
            q2.pop();
          }

          /*for(int i=1;i<w-1;i++){
            for(int j=1;j<h-1;j++){
              if(table[i][j] == rep){
                table[i][j] = com;
              }
            }
          }*/

        }
      }

      vec2 tmpvec = q1.front();
      q1.pop();
      int i = tmpvec.x;
      int j = tmpvec.y;

      if(i != 0 && i != w-1 && j != 0 && j != h-1){

        table[i][j] = com;
        for(int k=0;k<8;k++){
          int vi = i+dirx[k];
          int vj = j+diry[k];
          s[vi][vj]++;
        //  cout << ans  << " " << vi << " " << vj << " " << table[vi][vj] << " " << s[vi][vj] << endl;
          if(table[vi][vj] > 0 && s[vi][vj] == table[vi][vj]){
            vec2 tmpvecs(vi,vj);
            q2.push(tmpvecs);
            //table[vi][vj] = com;
          }

/*
          s[i+1][j]++;
          s[i+1][j-1]++;
          s[i+1][j+1]++;
          s[i][j-1]++;
          s[i][j+1]++;
          s[i-1][j]++;
          s[i-1][j+1]++;
          s[i-1][j-1]++;

          table[i][j] = com;
          vec2 tmpvec(i-1,j-1);
          q2.push(tmpvec);
          tmpvec.y++;
          q2.push(tmpvec);
          tmpvec.y++;
          q2.push(tmpvec);
          tmpvec.x++;tmpvec.y-=2;
          q2.push(tmpvec);
          tmpvec.y+=2;
          q2.push(tmpvec);
          tmpvec.x++;tmpvec.y-=2;
          q2.push(tmpvec);
          tmpvec.y++;
          q2.push(tmpvec);
          tmpvec.y++;
          q2.push(tmpvec);*/
        }
      }

    }



    cout << ans << endl;

    return 0;
}

Measured memory_bytes: 7104