The number of operations of Explicit and Implicit Euler for 1D hear equation I'm studying with "Numerical Solution of Partial Differential Equations by K.W.Morton and D.F.Mayers". On page 25, it says "2(add) + 2(multiply) operations per mesh point for the explicit algorithm (2.19)", but it seems 3(add) + 2(multiply) to me, how did I get wrong?

(2.19)  $U_j^{n+1}=U_j^{n}+\mu(U_{j+1}^{n}-2U_j^{n}+U_{j-1}^{n})$

My counting is 

2(add) and 1(multiply) inside the bracket

1(multiply) for $\mu$ and the brackets

1(add) for $U_j^{n}$ and the rest
Note that

$U^n_j + \mu (U^n_{j+1}-2U^n_j+U^n_{j-1}) = (1-2\mu)U^n_j+\mu(U^n_{j+1}+U^n_{j-1})$

$1-2\mu$ may be precomputed.