import java.util.*;

public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	String s = sc.next();
		String t = sc.next();
		int len = s.length();
		int count = 0;

		for(int i = 0; i < len; i++) {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		}
		System.out.println(count);
    }
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	String s = sc.next();
		String t = sc.next();
		int len = s.length();
		int count = 0;

		for(int i = 0; i < len; i++) {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		}
		System.out.println(count);
    }
} Main public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	String s = sc.next();
		String t = sc.next();
		int len = s.length();
		int count = 0;

		for(int i = 0; i < len; i++) {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		}
		System.out.println(count);
    } main {
    	Scanner sc = new Scanner(System.in);
    	String s = sc.next();
		String t = sc.next();
		int len = s.length();
		int count = 0;

		for(int i = 0; i < len; i++) {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		}
		System.out.println(count);
    } 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 int len = s.length(); len s.length() s.length s int count = 0; count 0 for(int i = 0; i < len; i++) {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		} int i = 0; int i = 0; i 0 i < len i len i++ i++ i {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		} {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		} char a = s.charAt(i); a s.charAt(i) s.charAt s i char b = t.charAt(i); b t.charAt(i) t.charAt t i if(a != b) {
				count++;
			} a != b a b {
				count++;
			} count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	String s = sc.next();
		String t = sc.next();
		int len = s.length();
		int count = 0;

		for(int i = 0; i < len; i++) {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		}
		System.out.println(count);
    }
} public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	String s = sc.next();
		String t = sc.next();
		int len = s.length();
		int count = 0;

		for(int i = 0; i < len; i++) {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		}
		System.out.println(count);
    }
} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	String s = sc.next();
		String t = sc.next();
		int len = s.length();
		int count = 0;

		for(int i = 0; i < len; i++) {
			char a = s.charAt(i);
			char b = t.charAt(i);
			if(a != b) {
				count++;
			}
		}
		System.out.println(count);
    }
}