The Knuth-Morris-Pratt (KMP) algorithm is a string-matching algorithm. Its core is the prefix function. Given a pattern $P[1..m]$, the prefix function for the pattern $P$ is the function $\pi:\{1,2,\ldots,m\}\to\{0,1,\ldots,m-1\}$. What is $\pi[7]$ for the following pattern $P$?

(A) 4 (B) 5 (C) 6 (D) 7