import java.util.HashMap;
import java.util.HashSet;
import java.util.Scanner;

public class Main {
	
	
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String k = s.next();
		String m = s.next();
		
		int n = k.length(),ctr=0;
		for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		}
		System.out.println(ctr);
	}

} import java.util.HashMap; HashMap java.util import java.util.HashSet; HashSet java.util import java.util.Scanner; Scanner java.util public class Main {
	
	
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String k = s.next();
		String m = s.next();
		
		int n = k.length(),ctr=0;
		for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		}
		System.out.println(ctr);
	}

} Main public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String k = s.next();
		String m = s.next();
		
		int n = k.length(),ctr=0;
		for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		}
		System.out.println(ctr);
	} main {
		Scanner s = new Scanner(System.in);
		String k = s.next();
		String m = s.next();
		
		int n = k.length(),ctr=0;
		for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		}
		System.out.println(ctr);
	} Scanner s = new Scanner(System.in); s new Scanner(System.in) String k = s.next(); k s.next() s.next s String m = s.next(); m s.next() s.next s int n = k.length() n k.length() k.length k ctr=0; ctr 0 for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		} {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		} if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			} k.charAt(i)!=m.charAt(i) k.charAt(i) k.charAt k i m.charAt(i) m.charAt m i {
				ctr++;
			} ctr++ ctr System.out.println(ctr) System.out.println System.out System System.out ctr String[] args args public class Main {
	
	
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String k = s.next();
		String m = s.next();
		
		int n = k.length(),ctr=0;
		for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		}
		System.out.println(ctr);
	}

} public class Main {
	
	
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String k = s.next();
		String m = s.next();
		
		int n = k.length(),ctr=0;
		for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		}
		System.out.println(ctr);
	}

} Main
import java.util.HashMap;
import java.util.HashSet;
import java.util.Scanner;

public class Main {
	
	
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String k = s.next();
		String m = s.next();
		
		int n = k.length(),ctr=0;
		for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		}
		System.out.println(ctr);
	}

}
