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 C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

namespace AtCoder.Question
{
    public class QuestionB
    {
        public static void Main(string[] args)
        {
            var s = ReadHelper.ReadValue<string>();
            var t = ReadHelper.ReadValue<string>();
            var count = 0;
            for (int i = 0; i < s.Length; i++)
            {
                if (s[i] != t[i])
                {
                    count++;
                }
            }
            Console.WriteLine(count);
        }

        static class ReadHelper
        {
            internal static T ReadValue<T>()
            {
                return (T)Convert.ChangeType(Console.ReadLine(), typeof(T));
            }
            internal static (T1, T2) ReadValue<T1, T2>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)));
            }
            internal static (T1, T2, T3) ReadValue<T1, T2, T3>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)), (T3)Convert.ChangeType(input[2], typeof(T3)));
            }
            internal static (T1, T2, T3, T4) ReadValue<T1, T2, T3, T4>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)), (T3)Convert.ChangeType(input[2], typeof(T3)), (T4)Convert.ChangeType(input[3], typeof(T4)));
            }
            internal static T[] ReadValues<T>()
            {
                var input = Console.ReadLine().Split(' ');
                return input.Select(x => (T)Convert.ChangeType(x, typeof(T))).ToArray();
            }
        }

        static class MathAlgorithm
        {
            internal static bool IsPrime(long n)
            {
                if (n == 2) return true;
                if (n < 2 || n % 2 == 0) return false;
                var sqrt = Math.Sqrt(n);
                for (int i = 3; i <= sqrt; i += 2) if (n % i == 0) return false;
                return true;
            }
            internal static IEnumerable<long> EnumeratePrimes(long n)
            {
                var i = 2L;
                while (i * i <= n)
                {
                    if (n % i == 0)
                    {
                        n /= i;
                        yield return i;
                    }
                    else
                    {
                        i += i == 2 ? 1 : 2;
                    }
                }
                if (n != 1) yield return n;
            }
        }
    }
}