import java.util.Scanner;

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

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