#include <string.h>
#include <stdio.h>

#define WHMAX	(100)
#define GUARD	(9999)

int spos;
int stack[WHMAX*WHMAX+100];

int board[WHMAX+5][WHMAX+5];
int board2[WHMAX+5][WHMAX+5];

int saiki(int nx, int ny, int num, int cnt){
	int i, ret = 0;
	int px[] = {-1, 0, 1, 0};
	int py[] = { 0,-1, 0, 1};
	
	board2[ny][nx] = cnt;
	board[ny][nx] = 0;
	
	for(i=0;i<4;i++){
		int next = board2[ny+py[i]][nx+px[i]];
		if(next == (board2[ny][nx]-1)){continue;}
		if(next != 0){
			ret = 1;
			break;
		}
		if(board[ny+py[i]][nx+px[i]] == GUARD){continue;}
		if(board[ny+py[i]][nx+px[i]] == num){
//			printf("%d %d %d %d %d %d \n", nx, ny, nx+px[i], ny+py[i], num, next, cnt);
			ret = saiki(nx+px[i], ny+py[i], num, cnt+1);
		}
		
		if(ret == 1){
			break;
		}
	}
	
	return ret;
}

int main(void){
	int i,j,W,H;
	int ret=0;
	
	for(i=0;i<WHMAX+5;i++){
		for(j=0;j<WHMAX+5;j++){
			board[i][j] = GUARD;
		}
	}
	
	scanf("%d %d", &W, &H);
	
	for(i=1;i<=H;i++){
		for(j=1;j<=W;j++){
			scanf("%d", &board[i][j]);
		}
	}
	
	for(i=1;i<=H;i++){
		for(j=1;j<=W;j++){
			int tmp;
			if(board[i][j] == 0){continue;}
			
			memset(board2, 0, sizeof(board2));
			tmp = board[i][j];
			ret = saiki(j,i,tmp, 2);
			
			if(ret == 1){
				i=H+5;
				j=W+5;
			}
		}
	}
	
	if(ret == 1){
		printf("possible\n");
	}else{
		printf("impossible\n");
	}
	return 0;
}