# 黒を平行移動2グループに分けられるか
# 平行移動(di, dj)で全探索

H, W = map(int, input().split())
S = []
S_num = []
for i in range(H):
    temp = input()
    S.append(temp)
    s = []
    for t in temp:
        if t == '.':
            s.append(0)
        else:
            s.append(1)
    S_num.append(s)

ans = 'NO'
for di in range(0, H):
    for dj in range(0, W):
        if (di, dj) == (0, 0):
            continue
        
        #print('di', di, 'dj', dj)
        color = [[0]*W for i in range(H)]
        bad = False
        for i in range(H-di):
            for j in range(W-dj):
                #print('i', i, 'j', j)
                if S_num[i][j] == 1 and color[i][j] == 0:
                    color[i][j] = 1
                    if color[i+di][j+dj] == 1:
                        bad = True
                    color[i+di][j+dj] = 1
        if S_num == color and bad == False:
            #print(di, dj, color)
            ans = 'YES'
print(ans)