easy

import java.util.Scanner;
public class Main {
    static char[] arr_c = new char[105];
    static int len;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        String str1 = sc.next();
        int ans=0;
        len = str.length();
        for (int i = 0; i < len; i++) {
            arr_c[i] = str.charAt(i);
        }

        for (int i = 0; i < len; i++) {
            if (arr_c[i] != str1.charAt(i)) {
                turn(i);
                ans++;
            }
        }
        System.out.println(ans);
    }

    public static void turn(int index){
        arr_c[index] = arr_c[index]=='*'?'o':'*';
        arr_c[index+1] = arr_c[index+1]=='*'?'o':'*';
    }
}