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>

int main()
{
    int n = 0;
    char S[30];
    char T[30];


    //標準入力から1行bufに格納
    if (fgets(S, sizeof(S), stdin)==S);
    if (fgets(T, sizeof(T), stdin)==S);

    size_t a = strlen(S);
    size_t b = strlen(T);

    for (int x=0; x<a; x++)
    if ((a<=200000 && a<=200000) && (((S[x])>='a') && ((S[x])<='z')) && (((T[x])>='a') && ((T[x])<='z')) && a==b)
    {for (int i=0; i<a; i++)
    {
        if (S[i]!=T[i])
        {
            n++;
        }
    }
    printf("%d\n", n);
    }
    return 0;
}