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 (GCC 9.2.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

int main()
{
    char buf[200000];
    char buf2[200000];
    int count = 0;

    fgets(buf, sizeof(buf), stdin);
    fgets(buf2, sizeof(buf2), stdin);

    if (buf == NULL) return 1; 
    if (buf2 == NULL) return 1; 

    if (sizeof(buf) != sizeof(buf2)){
        exit(1);
    }

    for (int i = 0; i < sizeof(strlen(buf)); i++){
        if(isalpha(buf[i]) && isalpha(buf2[i])){
            if (buf[i] != buf2[i]){
            buf[i] = buf2[i];
            count++;
            }
        } 
    }

    printf("%d\n", count);
    return 0;
}