print((function (n, m)
	for _=1,n do
		local s,t=io.stdin:read("*l"),0
		for i=1,#s do
			if t==3 then if s:sub(i,i)=="E" then return "YES" else t=0 end end
			if t==2 then if s:sub(i,i)=="V" then t=t+1 else t=0 end end
			if t==1 then if s:sub(i,i)=="O" then t=t+1 else t=0 end end
			if s:sub(i,i)=="L" then t=1 end
		end
	end
	return "NO"
end)(io.stdin:read("*n"), io.stdin:read("*l")))