import java.util.Scanner;
class Main{
    public static void main(String[] args) {
        Scanner sc =  new Scanner(System.in);
        String a=sc.next();
        String b=sc.next();
        System.out.println(ditui(a.toCharArray(),b.toCharArray()));
    }
    public static int ditui(char[] a,char[] b) {
        int result=0;
        for(int i=0;i<a.length;i++) {
            if(a[i]==b[i])continue;
            else {
                if(a[i+1]=='*')a[i+1]='o';
                else a[i+1]='*';
                result++;
            }
        }
        return result;
    }
}