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 Kotlin (1.3.71) (judge verdict: Accepted)

import java.io.BufferedReader
import java.io.IOException
import java.io.InputStreamReader
import java.util.*
import kotlin.collections.HashSet
import kotlin.math.*
fun main(){
    var fs = CodeForces.FastReader()
    var s = fs.next()
    var t = fs.next()
    var ans = 0
    for (i in 0 until s.length) {
        if(s[i] != t[i]) ans++
    }
    println(ans)
}

class CodeForces {
    internal class FastReader {
        private var br: BufferedReader = BufferedReader(InputStreamReader(System.`in`))
        private var st: StringTokenizer? = null

        operator fun next(): String {
            while (st == null || !st!!.hasMoreElements()) {
                try {
                    st = StringTokenizer(br.readLine())
                } catch (e: IOException) {
                    e.printStackTrace()
                }

            }
            return st!!.nextToken()
        }

        fun nextInt(): Int {
            return Integer.parseInt(next())
        }

        fun nextLong(): Long {
            return java.lang.Long.parseLong(next())
        }

        fun nextDouble(): Double {
            return java.lang.Double.parseDouble(next())
        }

        fun nextLine(): String {
            var str = ""
            try {
                str = br.readLine()
            } catch (e: IOException) {
                e.printStackTrace()
            }
            return str
        }

        fun readIntArray(n: Int): IntArray {
            val a = IntArray(n)
            for (i in 0 until n) a[i] = nextInt()
            return a
        }
        fun readLongArray(n: Int): LongArray {
            val a = LongArray(n)
            for (i in 0 until n) a[i] = nextLong()
            return a
        }

        fun readDoubleArray(n: Int): DoubleArray {
            val a = DoubleArray(n)
            for (i in 0 until n) a[i] = nextDouble()
            return a
        }
    }
}