import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		String b = sc.next();
		char[] d = a.toCharArray();
		char[] e = b.toCharArray();
		int r= 0;
		for(int i = 0;i < d.length;i++) {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		}
		System.out.println(r);
		sc.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		String b = sc.next();
		char[] d = a.toCharArray();
		char[] e = b.toCharArray();
		int r= 0;
		for(int i = 0;i < d.length;i++) {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		}
		System.out.println(r);
		sc.close();
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		String b = sc.next();
		char[] d = a.toCharArray();
		char[] e = b.toCharArray();
		int r= 0;
		for(int i = 0;i < d.length;i++) {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		}
		System.out.println(r);
		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		String b = sc.next();
		char[] d = a.toCharArray();
		char[] e = b.toCharArray();
		int r= 0;
		for(int i = 0;i < d.length;i++) {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		}
		System.out.println(r);
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String a = sc.next(); a sc.next() sc.next sc String b = sc.next(); b sc.next() sc.next sc char[] d = a.toCharArray(); d a.toCharArray() a.toCharArray a char[] e = b.toCharArray(); e b.toCharArray() b.toCharArray b int r= 0; r 0 for(int i = 0;i < d.length;i++) {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		} int i = 0; int i = 0; i 0 i < d.length i d.length d d.length i++ i++ i {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		} {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		} if(!(d[i]==(e[i]))) {
				r++;
			} !(d[i]==(e[i])) (d[i]==(e[i])) d[i] d i (e[i]) e i {
				r++;
			} r++ r System.out.println(r) System.out.println System.out System System.out r sc.close() sc.close sc String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		String b = sc.next();
		char[] d = a.toCharArray();
		char[] e = b.toCharArray();
		int r= 0;
		for(int i = 0;i < d.length;i++) {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		}
		System.out.println(r);
		sc.close();
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		String b = sc.next();
		char[] d = a.toCharArray();
		char[] e = b.toCharArray();
		int r= 0;
		for(int i = 0;i < d.length;i++) {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		}
		System.out.println(r);
		sc.close();
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		String b = sc.next();
		char[] d = a.toCharArray();
		char[] e = b.toCharArray();
		int r= 0;
		for(int i = 0;i < d.length;i++) {
			if(!(d[i]==(e[i]))) {
				r++;
			}
		}
		System.out.println(r);
		sc.close();
	}
}
