/*Function Template*/
#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> pint;
const int MAX = 510000;
const int MOD = 1000000007;
#define rep(i, n) for(ll i = 0; i < (n); i++)
#define Rep(i, n) for(ll i = 1; i < (n); i++)
#define ALL(a)  (a).begin(),(a).end()
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
ll fac[MAX], finv[MAX], inv[MAX];


template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (ll i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }

}
ll Len(ll n) {
  ll s=0;
  while(n!=0) s++, n/=10;
  return s;
}


ll Sint(ll n) {
  ll m=0,s=0,a=n;
  while(a!=0) s++, a/=10;
  for(ll i=s-1;i>=0;i--) m+=n/((ll)pow(10,i))-(n/((ll)pow(10,i+1)))*10;
  return m;
}


ll Svec(vector<ll> v){
  ll n=0;
  for(ll i=0;i<v.size();i++) n+=v[i];
  return n;
}


ll GCD(ll a,ll b) {
  return b ? GCD(b,a%b) : a;
}


ll LCM(ll a,ll b){
  return a/GCD(a,b)*b;
}


ll Factorial(ll n){
  ll m=1;
  while(n>=1) m*=n,n--;
  return m;
}

void runlength(string s,vector<pair<char,ll>> &p){
  ll x=1;
  if(s.size()==1){
    p.push_back(pair<char,ll>(s[0],1));
  }
  for(ll i=0;i<s.size()-1;i++){
    if(s[i]==s[i+1]){
      x++;
      if(i==s.size()-2){
        p.push_back(pair<char,ll>(s[i],x));
      }
    }else{
      p.push_back(pair<char,ll>(s[i],x));
      x=1;
      if(i==s.size()-2){
        p.push_back(pair<char,ll>(s[s.size()-1],x));
      }
    }
  }
}




ll COM(ll n,ll k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

const int MAX_N=100010;
vector<bool> sieve_of_eratosthenes(){
  vector<bool> isPrime(MAX_N+1,true);
  for(int i=2;i<=MAX_N;i++){
    if(isPrime[i]){
      for(int j=2*i;j<=MAX_N;j+=i){
        isPrime[j]=false;
      }
    }
  }
  return isPrime;
}

vector<pint> prime_factorize(ll n){
  vector<pint> ans;
  for(ll p=2;p<=sqrt(n);p++){
    if(n%p!=0) continue;
    ll cnt=0;
    while(n%p==0){
      n/=p;
      cnt++;
    }
    ans.push_back(make_pair(p,cnt));
  }
  if(n!=1) ans.push_back(make_pair(n,1));
  return ans;
}

/*↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓*/
int main() {
  IOS;
  ll h,w;
  cin>>h>>w;
  ll cnt=0;
  vector<vector<char>> v(h,vector<char>(w));
  bool flag=true;
  ll sx,sy;
  rep(i,h) rep(j,w) cin>>v[i][j];
  rep(i,h){
    rep(j,w){
      if(flag && v[i][j]=='#'){
        sx=j;
        sy=i;
        flag=false;
      }
      if(v[i][j]=='#') cnt++;
    }
  }
  ll cnt2=1;
  while(true){
    ll left=sx-1,right=sx+1,up=sy-1,down=sy+1;
    ll counter1=0;
    ll counter2=0;
    if(left>=0) if(v[sy][left]=='#') counter1++;
    if(right<w) if(v[sy][right]=='#') counter2++;
    if(up>=0) if(v[up][sx]=='#') counter1++;
    if(down<h) if(v[down][sx]=='#') counter2++;
    if(counter1>=2 || counter2>=2){
      cout<<"Impossible"<<endl;
      return 0;
    }else{
      ll ttmp=0;
      ll dx=0;
      ll dy=0;
      if(right<w){
        if(v[sy][right]=='#') dx++;
        else ttmp++;
      }else{
        ttmp++;
      }
      if(down<h){
        if(v[down][sx]=='#') dy++;
        else ttmp++;
      }else{
        ttmp++;
      }
      sx+=dx;
      sy+=dy;
      if(ttmp==2){
        if(cnt==cnt2){
          cout<<"Possible"<<endl;
          return 0;
        }else{
          cout<<"Impossible"<<endl;
          return 0;
        }
      }
      cnt2++;
      
    }
  }
}

Measured memory_bytes: 256