H, W = map(int, input().split())
grid = [input() for i in range(H)]

for tatehoukounoshift in range(H):
    for yokohoukounoshift in range(W):
        if tatehoukounoshift == yokohoukounoshift == 0:
            continue
        can = True
        used = [[False] * W for i in range(H)]
        for i in range(H):
            for j in range(W):
                if used[i][j] or grid[i][j] == ".":
                    continue
                if not (0 <= i + tatehoukounoshift < H and 0 <= j + yokohoukounoshift < W):
                    can = False
                    break
                if grid[i + tatehoukounoshift][j + yokohoukounoshift] == ".":
                    can = False
                used[i][j] = True
                used[i + tatehoukounoshift][j + yokohoukounoshift] = True
        if can:
            print("YES")
            exit()
print("NO")