#include "bits/stdc++.h"
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define REP(i,a) for(int i=0;i<a;i++)
#define printall(n,array) for(int i=0;i<n;i++){cout<<array[i]<<" ";}cout<<endl;
#define U() cout<<endl;
typedef long long ll;
typedef pair<int, int> PI;
typedef pair<int, PI> V;
typedef vector<int> VE;
const ll mod = 1000000007; //10^9+7

int w,h;
int m[102][102];
int cp[102][102];
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};


bool check(int y,int x, int _){
  if((y>=0&&y<h&&x>=0&&x<w)&&(cp[y][x]==_||cp[y][x]==0))return true;
  return false;
}


int main(){
  cin>>w>>h;
  REP(i,h)REP(j,w)cin>>m[i][j];
  ////REP(i,h){REP(j,w)cout<<m[i][j]<<" ";cout<<endl;}///
  REP(_,1001){
    REP(i,h)REP(j,w)cp[i][j]=m[i][j];
    REP(i,h)REP(j,w)if(cp[i][j]==_){
      cp[i][j]=0;
      queue<V> que;
      //print("new x y"<<" "<<j<<" "<<i);///
      REP(k,4){
        int ny=i+dy[k];
        int nx=j+dx[k];
        if(check(ny,nx,_)==false)continue;
        cp[ny][nx]=0;
        V now=make_pair(k,make_pair(ny,nx));
        que.push(now);
        //print("push x y"<<" "<<nx<<" "<<ny);///
      }
      //U();///
      while(!que.empty()){
        V pre=que.front();
        PI pred=pre.second;
        que.pop();
        //print("now x y"<<" "<<pred.second<<" "<<pred.first);///
        REP(k,4){
          if(k==(pre.first+2)%4)continue;
          int ny=pred.first+dy[k];
          int nx=pred.second+dx[k];
          if(check(ny,nx,_)==0)continue;
          //print("k "<<k);///
          //print(nx<<" "<<ny);///
          //U();///
          if(cp[ny][nx]==0){
            //print("_ "<<_);///
            //REP(i,h){REP(j,w)cout<<cp[i][j]<<" ";cout<<endl;}///     
            //U();///
            print("possible");
            return 0;
          }
          if(cp[ny][nx]==_){
          cp[ny][nx]=0;
          V next=make_pair(k,make_pair(ny,nx));
          que.push(next);
          ////print("k "<<k);///
          //REP(i,h){REP(j,w)cout<<cp[i][j]<<" ";cout<<endl;}///     
          //U();///
          }
        }
      }
      //print("asdf");///
      //print("_ "<<_);///
      //REP(i,h){REP(j,w)cout<<cp[i][j]<<" ";cout<<endl;}///     
      //U();///
    }
  }
  print("impossible");
}