#include <algorithm>
#include <cmath>
#include <cstring>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <iterator>

//#define pb push_back
//#define puts(x) cout << #x << " : " << x << endl;
//#pragma GCC diagnostic ignored "-Wconversion"
//#define REP(i,n) for (int i=0;i<(n);i++)
//#define REPE(i,n) for (int i=0;i<=(n);i++)
//#define init(a,b) memset((a), (b), (sizeof(a)));
//#define PI 3.14159265
//#define EPS (1e-10)
//#define EQ(a,b) (abs((a)-(b)) < EPS)

using namespace std;

typedef long long ll;
//#define int long long

int dxy[] = {0, 1, 0, -1, 0};

typedef pair<int, int> P;

int W, H;
int mp[200][200];

bool vis[200][200];

bool solve2(int num, int prevh, int prevw, int h, int w){
    for (int i=0;i<4;i++){
        int nh = h + dxy[i];
        int nw = w + dxy[i+1];
        if(nh == prevh && nw == prevw)continue;
        if(0<=nh&&nh<H&&0<=nw&&nw<W&&num==mp[nh][nw]){
            if(vis[nh][nw])return true;
            vis[nh][nw]=1;
            if(solve2(num, h, w, nh, nw)){
                return true;
            }
        }
    }
    return false;
}

bool solve(){
    for(int h=0;h<H;h++){
        for(int w=0;w<W;w++){
            if(!vis[h][w]){
                vis[h][w]=1;
                if (solve2(mp[h][w], -1, -1, h, w)){
                    return true;
                }
            }
        }
    }
    return false;
}

signed main() {
    cin>>W>>H;
    for(int h=0;h<H;h++){
        for(int w=0;w<W;w++){
            cin>>mp[h][w];
        }
    }
    if(solve()){
        cout<<"possible"<<endl;
    }else{
        cout<<"impossible"<<endl;

    }
    return 0;
}