import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		String[] ss = S.split("");
		String[] tt = T.split("");
		int res = 0;
		for (int i = 0; i < ss.length; i++) {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		}
		System.out.println(res);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		String[] ss = S.split("");
		String[] tt = T.split("");
		int res = 0;
		for (int i = 0; i < ss.length; i++) {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		}
		System.out.println(res);
	}
} Main public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		String[] ss = S.split("");
		String[] tt = T.split("");
		int res = 0;
		for (int i = 0; i < ss.length; i++) {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		}
		System.out.println(res);
	} main {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		String[] ss = S.split("");
		String[] tt = T.split("");
		int res = 0;
		for (int i = 0; i < ss.length; i++) {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		}
		System.out.println(res);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.next(); S sc.next() sc.next sc String T = sc.next(); T sc.next() sc.next sc String[] ss = S.split(""); ss S.split("") S.split S "" String[] tt = T.split(""); tt T.split("") T.split T "" int res = 0; res 0 for (int i = 0; i < ss.length; i++) {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		} int i = 0; int i = 0; i 0 i < ss.length i ss.length ss ss.length i++ i++ i {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		} {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		} if (!ss[i].equals(tt[i])) {
				res++;
			} !ss[i].equals(tt[i]) ss[i].equals(tt[i]) ss[i].equals ss[i] ss i tt[i] tt i {
				res++;
			} res++ res System.out.println(res) System.out.println System.out System System.out res String[] args args public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		String[] ss = S.split("");
		String[] tt = T.split("");
		int res = 0;
		for (int i = 0; i < ss.length; i++) {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		}
		System.out.println(res);
	}
} public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		String[] ss = S.split("");
		String[] tt = T.split("");
		int res = 0;
		for (int i = 0; i < ss.length; i++) {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		}
		System.out.println(res);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		String[] ss = S.split("");
		String[] tt = T.split("");
		int res = 0;
		for (int i = 0; i < ss.length; i++) {
			if (!ss[i].equals(tt[i])) {
				res++;
			}
		}
		System.out.println(res);
	}
}