Problem:
Score : 200 points

Problem Statement

#nck {
width: 30px;
height: auto;
}

We have a grid of H rows and W columns. Initially, there is a stone in the top left cell. Shik is trying to move the stone to the bottom right cell. In each step, he can move the stone one cell to its left, up, right, or down (if such cell exists). It is possible that the stone visits a cell multiple times (including the bottom right and the top left cell).

You are given a matrix of characters a_{ij} (1 \leq i \leq H, 1 \leq j \leq W). After Shik completes all moving actions, a_{ij} is # if the stone had ever located at the i-th row and the j-th column during the process of moving. Otherwise, a_{ij} is .. Please determine whether it is possible that Shik only uses right and down moves in all steps.

Constraints

2 \leq H, W \leq 8

a_{i,j} is either # or ..

There exists a valid sequence of moves for Shik to generate the map a.

Input

The input is given from Standard Input in the following format:

H W
a_{11}a_{12}...a_{1W}
:
a_{H1}a_{H2}...a_{HW}

Output

If it is possible that Shik only uses right and down moves, print Possible. Otherwise, print Impossible.

Sample Input 1

4 5
##...
.##..
..##.
...##

Sample Output 1

Possible

The matrix can be generated by a 7-move sequence: right, down, right, down, right, down, and right.

Sample Input 2

5 3
###
..#
###
#..
###

Sample Output 2

Impossible

Sample Input 3

4 5
##...
.###.
.###.
...##

Sample Output 3

Impossible

Solution in C++ (GCC 9.2.1) (judge verdict: Accepted)

#include<algorithm>
#include<bitset>
#include<cmath>
#include<complex>
#include<deque>
#include<functional>
#include<iomanip>
#include<iostream>
#include<iterator>
#include<map>
#include<numeric>
#include<queue>
#include<set>
#include<stack>
#include<string>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>

using namespace std;
typedef long long ll;

#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define REPD(i,n) for(ll i=n-1;i>=0;i--)
#define FOR(i,a,b) for(ll i=a;i<=(ll)(b);i++)
#define FORD(i,a,b) for(ll i=a;i>=(ll)(b);i--)
#define ALL(x) (x).begin(),(x).end()
#define SIZE(x) ((ll)(x).size())
#define MAX(x) *max_element(ALL(x))
#define MIN(x) *min_element(ALL(x))
#define D()
#define INF 1000000000000
#define MOD 10000007
#define MAXR 100000
#define PB push_back
#define MP make_pair
#define F first
#define S second
#define INITA(a,i,j,v) for(ll k=i;k<=j;k++){a[k]=v;}

int main() {
    int h, w; cin >> h >> w;
    string a[10];
    REP(i, h) {
        cin >> a[i];
    }
    REP(i, h) {
        REP(j, w) {
            if (((i == h - 1) && (j == w - 1))) {
                // 最初のマス、最後のマスについては二方向に '#' がある場合はNG
                if ((a[i-1][j] == '#') && (a[i][j-1] == '#')) {
                    cout << "Impossible" << endl;
                    return 0;
                }
            } else if ((a[i][j] == '#') && (a[i+1][j] != '#') && (a[i][j+1] != '#')) {
                // 終点以外のすべての通過マスについて、右も下も '.' だとNG
                cout << "Impossible" << endl;
                return 0;
            } else {
                // 三方向に '#' がある場合はNG
                int c = 0;
                if ((0 < i) && (a[i-1][j] == '#')) {
                    c++;
                }
                if ((i < h - 1) && (a[i+1][j] == '#')) {
                    c++;
                }
                if ((0 < j) && (a[i][j-1] == '#')) {
                    c++;
                }
                if ((j < w - 1) && (a[i][j+1] == '#')) {
                    c++;
                }
                if (c > 2) {
                    cout << "Impossible" << endl;
                    return 0;
                }

                // 最初のマス、最後のマスについては二方向に '#' がある場合はNG
                if ((i == 0) && (j == 0) && (a[i+1][j] == '#') && (a[i][j+1] == '#')) {
                    cout << "Impossible" << endl;
                    return 0;
                }
                if ((i == h-1) && (j == w-1) && (a[i-1][j] == '#') && (a[i][j-1] == '#')) {
                    cout << "Impossible" << endl;
                    return 0;
                }
            }
        }
    }
    cout << "Possible" << endl;
    return 0;
}