Suppose v is starting vertex so start DFS at node v
(i) visit t (v) → DFS(A) → visit (A) → DFS
(v) → visit (u) → back track (A) → Back track (v)
therefore d[v] > d[v], d[v] < f[v] f[v] < f[v]
But visiting order is just opposite of finishing order.
Hence f[v] > f[v]
Maximum DFS recurside depth is 19
A → B → C → D → E → F → G → H → I → J → K
→ L → M → N → O → P → Q → R → S