	import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Scanner;
import java.util.Set;
	
	public class Main {
	
		public static void main(String[] args) {
			execute16_3();
		}
		
		private static void execute16_3() {
			try 
			(Scanner sc = new Scanner(System.in)) {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			}
			
		}
    } import java.util.ArrayDeque; ArrayDeque java.util import java.util.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.Comparator; Comparator java.util import java.util.Deque; Deque java.util import java.util.HashMap; HashMap java.util import java.util.HashSet; HashSet java.util import java.util.List; List java.util import java.util.Map; Map java.util import java.util.Queue; Queue java.util import java.util.Scanner; Scanner java.util import java.util.Set; Set java.util public class Main {
	
		public static void main(String[] args) {
			execute16_3();
		}
		
		private static void execute16_3() {
			try 
			(Scanner sc = new Scanner(System.in)) {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			}
			
		}
    } Main public static void main(String[] args) {
			execute16_3();
		} main {
			execute16_3();
		} execute16_3() execute16_3 String[] args args private static void execute16_3() {
			try 
			(Scanner sc = new Scanner(System.in)) {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			}
			
		} execute16_3 {
			try 
			(Scanner sc = new Scanner(System.in)) {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			}
			
		} try 
			(Scanner sc = new Scanner(System.in)) {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			} {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			} Scanner sc = new Scanner(System.in) Scanner sc = new Scanner(System.in) 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 ans=0; ans 0 for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			} int i=0; int i=0; i 0 i<s.length() i s.length() s.length s i++ i++ i {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			} {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			} if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				} s.charAt(i)!=t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i {
					ans++;
				} ans++ ans System.out.println(ans) System.out.println System.out System System.out ans public class Main {
	
		public static void main(String[] args) {
			execute16_3();
		}
		
		private static void execute16_3() {
			try 
			(Scanner sc = new Scanner(System.in)) {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			}
			
		}
    } public class Main {
	
		public static void main(String[] args) {
			execute16_3();
		}
		
		private static void execute16_3() {
			try 
			(Scanner sc = new Scanner(System.in)) {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			}
			
		}
    } Main
	import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Scanner;
import java.util.Set;
	
	public class Main {
	
		public static void main(String[] args) {
			execute16_3();
		}
		
		private static void execute16_3() {
			try 
			(Scanner sc = new Scanner(System.in)) {
				String s = sc.next();
				String t = sc.next();
			
			int ans=0;
			
			for(int i=0; i<s.length(); i++) {
				if(s.charAt(i)!=t.charAt(i)) {
					ans++;
				}
			}
			System.out.println(ans);
			}
			
		}
    }