#include <queue>
#include <algorithm>
#include <vector>
#include <iostream>
#include <numeric>
#include <tuple>
using namespace std;
typedef long long int ll;
typedef pair<int, int> pii;
typedef tuple<int, int, int> tiii;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define ALL(container) (container).begin(), (container).end()

int f[200][200];
int visit[200][200];

int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    int w,h;
    cin >> w >> h;
    REP(i, 200) REP(j, 200) f[i][j] = 0;
    REP(i, 200) REP(j, 200) visit[i][j] = 0;
    
    REP(i, h) REP(j, w)
    {
        int v;
        cin >> v;
        f[i+1][j+1] = v;
    }

    pii shifts[] = {{1,0},{0,1},{-1,0},{0,-1}};
    REP(i, h) REP(j, w)
    {
        int sh = i + 1;
        int sw = j + 1;
        REP(k, 200) REP(l, 200) visit[k][l] = 0;
        queue<tiii> q;
        q.push(make_tuple(sw,sh,-1));
        visit[sh][sw] = 1;
        int num = f[sh][sw];
        while(!q.empty())
        {
            const auto t = q.front();
            q.pop();
            int current = visit[get<1>(t)][get<0>(t)];
            for(int s = 0;s < 4;s++)
            {
                if(s == get<2>(t))
                {
                    continue;
                }
                auto x = get<0>(t) + shifts[s].first;
                auto y = get<1>(t) + shifts[s].second;
                if(f[y][x] != num)
                {
                    continue;
                }
                if(visit[y][x])
                {
                    cout << "possible" << endl;
                    return 0;
                }
                else
                {
                    visit[y][x] = current + 1;
                    q.push(make_tuple(x,y,(s + 2) % 4));
                }
            }
        }
    }
    cout << "impossible" << endl;
    return 0;
}