#include <iostream>
#include <algorithm>
#include <array>
#include <queue>
#include <tuple>
using namespace std;
                            // N  E  S  W
constexpr array<int, 4> dr = {-1, 0, 1, 0},
                        dc = { 0, 1, 0,-1};
constexpr int dr_size = dr.size();

int main(void) {
  int C, R; scanf("%d%d", &C, &R);
  vector<vector<int>> G(R, vector<int>(C, 0)); // G[R][C]
  for(int r=0; r<R; ++r) {
    for(int c=0; c<C; ++c) {
      scanf("%d", &G[r][c]);
    }
  }
  for(int r=0; r<R; ++r) { // (r, c) := 始点
    for(int c=0; c<C; ++c) {
      int val = G[r][c];
      vector<vector<bool>> seen(R, vector<bool>(C, false)); // seen[R][C]
      queue<tuple<int, int, int, int>> que;
      // 今の座標、ひとつ前の座標
      que.emplace(r, c, -1, -1);
      while(!que.empty()) {
        int rr, cc, br, bc; tie(rr, cc, br, bc) = que.front(); que.pop();
        for(int i=0; i<dr_size; ++i) {
          int nr = rr + dr[i],
              nc = cc + dc[i];
          if(!(0 <= nr && nr < R && 0 <= nc && nc < C)) { continue; }
          if(G[nr][nc] != val) { continue; }
          if(nr == br && nc == bc) { continue; }
          if(seen[nr][nc]) { continue; }
          if(nr == r && nc == c) {
            puts("possible");
            return 0;
          }
          seen[nr][nc] = true;
          que.emplace(nr, nc, rr, cc);
          seen[nr][nc] = false;
        }
      }
    }
  }
  puts("impossible");
  return 0;
}