HMAC(K,C) = SHA1(K ⊕ 0x5c5c… ∥ SHA1(K ⊕ 0x3636… ∥C))

The basic idea I get and I'm thinking⊕means something like plus. What are the two vertical lines. (K is a pre-defined but arbitrary value and C is a counter.)

The wikipedia math symbol page is helping much