import java.util.*;
 
public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = (int)1e9 + 7;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	int len = (int)1e7;
	
	
	void doIt() {
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		int len = S.length;
		int sum = 0;
		for(int i = 0; i < len; i++) {
			if(S[i] != T[i])sum++;
		}
		System.out.println(sum);
	}
	
	public static void main(String[] args) {
		new Main().doIt();
	}
 
} import java.util.*; util.* java public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = (int)1e9 + 7;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	int len = (int)1e7;
	
	
	void doIt() {
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		int len = S.length;
		int sum = 0;
		for(int i = 0; i < len; i++) {
			if(S[i] != T[i])sum++;
		}
		System.out.println(sum);
	}
	
	public static void main(String[] args) {
		new Main().doIt();
	}
 
} Main Scanner sc = new Scanner(System.in); sc new Scanner(System.in) final int MOD = (int)1e9 + 7; MOD (int)1e9 + 7 (int)1e9 7 final int MAX = Integer.MAX_VALUE; MAX Integer.MAX_VALUE Integer Integer.MAX_VALUE final long LMAX = Long.MAX_VALUE; LMAX Long.MAX_VALUE Long Long.MAX_VALUE int len = (int)1e7; len (int)1e7 void doIt() {
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		int len = S.length;
		int sum = 0;
		for(int i = 0; i < len; i++) {
			if(S[i] != T[i])sum++;
		}
		System.out.println(sum);
	} doIt {
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		int len = S.length;
		int sum = 0;
		for(int i = 0; i < len; i++) {
			if(S[i] != T[i])sum++;
		}
		System.out.println(sum);
	} char[] S = sc.next().toCharArray(); S sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc char[] T = sc.next().toCharArray(); T sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc int len = S.length; len S.length S S.length int sum = 0; sum 0 for(int i = 0; i < len; i++) {
			if(S[i] != T[i])sum++;
		} int i = 0; int i = 0; i 0 i < len i len i++ i++ i {
			if(S[i] != T[i])sum++;
		} {
			if(S[i] != T[i])sum++;
		} if(S[i] != T[i])sum++; S[i] != T[i] S[i] S i T[i] T i sum++ sum System.out.println(sum) System.out.println System.out System System.out sum public static void main(String[] args) {
		new Main().doIt();
	} main {
		new Main().doIt();
	} new Main().doIt() new Main().doIt new Main() String[] args args public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = (int)1e9 + 7;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	int len = (int)1e7;
	
	
	void doIt() {
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		int len = S.length;
		int sum = 0;
		for(int i = 0; i < len; i++) {
			if(S[i] != T[i])sum++;
		}
		System.out.println(sum);
	}
	
	public static void main(String[] args) {
		new Main().doIt();
	}
 
} public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = (int)1e9 + 7;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	int len = (int)1e7;
	
	
	void doIt() {
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		int len = S.length;
		int sum = 0;
		for(int i = 0; i < len; i++) {
			if(S[i] != T[i])sum++;
		}
		System.out.println(sum);
	}
	
	public static void main(String[] args) {
		new Main().doIt();
	}
 
} Main
import java.util.*;
 
public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = (int)1e9 + 7;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	int len = (int)1e7;
	
	
	void doIt() {
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		int len = S.length;
		int sum = 0;
		for(int i = 0; i < len; i++) {
			if(S[i] != T[i])sum++;
		}
		System.out.println(sum);
	}
	
	public static void main(String[] args) {
		new Main().doIt();
	}
 
}