H,W=gets.split.map(&:to_i)
S=Array.new(H)

for i in 0...H do
    S[i]=gets.chomp
end

CAN=false

for i in 0...H do
    for j in 0...W do
        next if i==0 && j==0
        COIN=true
        
        T=Array.new(H).map{Array.new(W,0)}
        for ii in 0...H do
            for jj in 0...W do
                T[ii][jj]=1 if S[ii][jj]=='#'
            end
        end
        
        for ii in 0...H do
            for jj in 0...W do
                if T[ii][jj]==1
                    if ii+i>=H || jj+j>=W
                        COIN=false
                        next
                    end
                    COIN=false if T[ii+i][jj+j]!=1
                    T[ii][jj]=0
                    T[ii+i][jj+j]=0
                end
            end
        end
        
        CAN=true if COIN
    end
end

puts CAN ? "YES":"NO"