#include<bits/stdc++.h>
typedef uint64_t u64;
typedef int64_t i64;
using namespace std;

void solve();

int main(){
  cout<<fixed<<setprecision(15);
  bool is_multicase=false;
  int T=1;
  if(is_multicase){
    cin>>T;
  }
  for(int i=0;i<T;++i){
    solve();
  }
  return 0;
}

template<typename T> void turtle_in(T& n){
  cin>>n;
}

template<typename T,typename U> void turtle_in(pair<T,U>& p){
  turtle_in(p.first);
  turtle_in(p.second);
}

template<typename T> void turtle_in(vector<T>& v){
  for(auto& u:v){
    turtle_in(u);
  }
}

template<typename T> void turtle_out(T& n){
  cout<<n;
}

template<typename T,typename U> void turtle_out(pair<T,U>& p){
  cout<<"{";
  turtle_out(p.first);
  cout<<", ";
  turtle_out(p.second);
  cout<<"}";
}

template<typename T> void turtle_out(vector<T>& v){
  for(int i=0;i<int(v.size());++i){
    turtle_out(v[i]);
    if(i!=v.size()-1){
      cout<<" ";
    }
  }
  cout<<endl;
}

template<typename T> void turtle_out(vector<vector<T>>& v){
  for(int i=0;i<int(v.size());++i){
    turtle_out(v[i]);
  }
}

void scan(){}

template<typename T,class... Args> void scan(T& n,Args&... args){
  turtle_in(n);
  scan(args...);
}

void print(){}

template<typename T,class... Args> void print(T n,Args... args){
  turtle_out(n);
  print(args...);
}

template<typename T> void println(T n){
  turtle_out(n);
  cout<<endl;
}

template<typename T,class... Args> void println(T n,Args... args){
  turtle_out(n);
  cout<<" ";
  println(args...);
}

template<u64 mod> struct modint{
  u64 val;
  modint(i64 val_=0):val((val_%i64(mod)+i64(mod))%i64(mod)){}
  modint operator-(){
    return modint(mod-val);
  }
  modint operator+(modint rhs){
    return modint(*this)+=rhs;
  }
  modint operator-(modint rhs){
    return modint(*this)-=rhs;
  }
  modint operator*(modint rhs){
    return modint(*this)*=rhs;
  }
  modint operator/(modint rhs){
    return modint(*this)/=rhs;
  }
  modint &operator+=(modint rhs){
    val+=rhs.val;
    val-=((val>=mod)?mod:0);
    return (*this);
  }
  modint &operator-=(modint rhs){
    val+=((val<rhs.val)?mod:0);
    val-=rhs.val;
    return (*this);
  }
  modint &operator*=(modint rhs){
    val=val*rhs.val%mod;
    return (*this);
  }
  modint &operator/=(modint rhs){
    u64 ex=mod-2;
    modint now=1;
    while(ex){
      now*=((ex&1)?rhs:1);
      rhs*=rhs,ex>>=1;
    }
    return (*this)*=now;
  }
  bool operator==(modint rhs){
    return val==rhs.val;
  }
  bool operator!=(modint rhs){
    return val!=rhs.val;
  }
  friend std::ostream &operator<<(std::ostream& os,modint x){
    return os<<(x.val);
  }
  friend std::istream &operator>>(std::istream& is,modint& x){
    u64 t;
    is>>t,x=t;
    return is;
  }
};

template<typename T,typename U> T power(T a,U n){
  T res=1;
  while(n>0){
    if(n%2==1){
      res*=a;
    }
    a*=a;
    n/=2;
  }
  return res;
}

template<typename T> struct genrand{
  uniform_int_distribution<T> gen;
  mt19937 engine;
  genrand(T a,T b):gen(a,b){
    random_device seed_gen;
    engine.seed(seed_gen());
  }
  T operator()(){
    return gen(engine);
  }
};

template<typename T> struct comb{
  vector<T> dat,idat;
  comb(int mx=3000000):dat(mx+1,1),idat(mx+1,1){
    for(int i=1;i<=mx;++i){
      dat[i]=dat[i-1]*i;
    }
    idat[mx]/=dat[mx];
    for(int i=mx;i>0;--i){
      idat[i-1]=idat[i]*i;
    }
  }
  T operator()(int n,int k){
    if(n<0||k<0||n<k){
      return 0;
    }
    return dat[n]*idat[k]*idat[n-k];
  }
};

void solve(){
  int H,W;
  scan(H,W);
  vector<string> S(H);
  scan(S);
  vector<pair<int,int>> all;
  for(int i=0;i<H;++i){
    for(int j=0;j<W;++j){
      if(S[i][j]=='#'){
        all.emplace_back(i,j);
      }
    }
  }
  if(all.size()==0){
    println("NO");
    return;
  }
  for(int I=0;I<=H-1;++I){
    for(int J=-W+1;J<=W-1;++J){
      if(I==0 && J==0){
        continue;
      }
      if(I!=1||J!=1){
        continue;
      }
      map<pair<int,int>,vector<int>> tmp;
      if(I!=0){
        for(auto p:all){
          int i=p.first,j=p.second;
          tmp[{i%I,j-(i/I)*J}].emplace_back(i/I);
        }
      }
      else{
        int J_=-J,I_=-I;
        if(J_<0){
          J_=J,I_=I;
        }
        for(auto p:all){
          int i=p.first,j=p.second;
          tmp[{i-(j/J_)*I,j%J_}].emplace_back(j/J_);
        }
      }
      bool f=1;
      for(auto [_,v]:tmp){
        while(2<=v.size()){
          int n=v.size();
          if(v[n-2]+1==v[n-1]){
            v.resize(n-2);
          }
          else{
            break;
          }
        }
        if(v.size()!=0){
          f=0;
        }
      }
      if(f){
        println("YES");
        return;
      }
    }
  }
  println("NO");
}