S=input().split(' ')
n=int(S[0])
m=int(S[1])

for i in range(n):
    A=input()
    for j in range(m-3):
        if(A[j]=='L' and A[j+1]=='O' and A[j+2]=='V' and A[j+3]=='E'):
           print('YES')
           break
if(j==m-4):
   print('NO')