Problem:
Score : 200 points

Problem Statement

Given are strings S and T. Consider changing S to T by repeating the operation below. Find the minimum number of operations required to do so.

Operation: Choose one character of S and replace it with a different character.

Constraints

S and T have lengths between 1 and 2\times 10^5 (inclusive).

S and T consists of lowercase English letters.

S and T have equal lengths.

Input

Input is given from Standard Input in the following format:

S
T

Output

Print the answer.

Sample Input 1

cupofcoffee
cupofhottea

Sample Output 1

4

We can achieve the objective in four operations, such as the following:

First, replace the sixth character c with h.

Second, replace the eighth character f with t.

Third, replace the ninth character f with t.

Fourth, replace the eleventh character e with a.

Sample Input 2

abcde
bcdea

Sample Output 2

5

Sample Input 3

apple
apple

Sample Output 3

0

No operations may be needed to achieve the objective.

Solution in OCaml (4.10.0) (judge verdict: Accepted)

open Scanf
open Printf

let () =
  let s,t = scanf "%s %s" (fun s t -> (s, t)) in
  let s_length = String.length s in
  let rec loop s t i =
    if i > s_length -1 then 0
    else if s.[i] <> t.[i] then 1 + loop s t (i + 1)
                           else loop s t (i + 1)
  in
    printf "%d\n" (loop s t 0)