n, m = map(int, input().split())
g = [input() for i in range(n)]
def can_photo(color):
row_bad = [0] * n
col_bad = [0] * m
total = 0
for i in range(n):
for j in range(m):
if g[i][j] != color:
row_bad[i] += 1
col_bad[j] += 1
total += 1
for i in range(n):
for j in range(m):
removed = row_bad[i] + col_bad[j]
if g[i][j] != color:
removed -= 1 # клітинка (i, j) була врахована двічі
if removed == total:
return True
return False
if can_photo('Y') or can_photo('B'):
print("Yes")
else:
print("No")
