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 Rust (1.42.0) (judge verdict: Accepted)

use std::io;
use std::str;

/// Reads white-space separated tokens one at a time.
pub struct Scanner<R> {
    reader: R,
    buffer: Vec<String>,
}

impl<R: io::BufRead> Scanner<R> {
    pub fn new(reader: R) -> Self {
        Self {
            reader,
            buffer: vec![],
        }
    }

    /// Use "turbofish" syntax token::<T>() to select data type of next token.
    ///
    /// # Panics
    ///
    /// Panics if there's an I/O error or if the token cannot be parsed as T.
    pub fn token<T: str::FromStr>(&mut self) -> T {
        loop {
            if let Some(token) = self.buffer.pop() {
                return token.parse().ok().expect("Failed parse");
            }
            let mut input = String::new();
            self.reader.read_line(&mut input).expect("Failed read");
            self.buffer = input.split_whitespace().rev().map(String::from).collect();
        }
    }
}

fn solve<R: io::BufRead, W: io::Write>(scan: &mut Scanner<R>, out: &mut W) {
    let s: String = scan.token();
    let t: String = scan.token();
    let mut ans = 0;
    for it in s.chars().zip(t.chars()) {
        let (cs, ct) = it;
        if cs != ct {
            ans += 1;
        }
    }
    writeln!(out, "{}", ans).ok();
}

fn main() {
    let (stdin, stdout) = (io::stdin(), io::stdout());
    let mut scan = Scanner::new(stdin.lock());
    let mut out = io::BufWriter::new(stdout.lock());
    solve(&mut scan, &mut out);
}