import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);// TODO Auto-generated method stub
		String s=input.next();
		String t=input.next();
		char[] s1=s.toCharArray();
		char[] t1=t.toCharArray();
		int suma=0;
		for(int i=0;i<s.length();i++) {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		}
		System.out.println(suma);
			
	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);// TODO Auto-generated method stub
		String s=input.next();
		String t=input.next();
		char[] s1=s.toCharArray();
		char[] t1=t.toCharArray();
		int suma=0;
		for(int i=0;i<s.length();i++) {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		}
		System.out.println(suma);
			
	}

} Main public static void main(String[] args) {
		Scanner input=new Scanner(System.in);// TODO Auto-generated method stub
		String s=input.next();
		String t=input.next();
		char[] s1=s.toCharArray();
		char[] t1=t.toCharArray();
		int suma=0;
		for(int i=0;i<s.length();i++) {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		}
		System.out.println(suma);
			
	} main {
		Scanner input=new Scanner(System.in);// TODO Auto-generated method stub
		String s=input.next();
		String t=input.next();
		char[] s1=s.toCharArray();
		char[] t1=t.toCharArray();
		int suma=0;
		for(int i=0;i<s.length();i++) {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		}
		System.out.println(suma);
			
	} Scanner input=new Scanner(System.in); input new Scanner(System.in) String s=input.next(); s input.next() input.next input String t=input.next(); t input.next() input.next input char[] s1=s.toCharArray(); s1 s.toCharArray() s.toCharArray s char[] t1=t.toCharArray(); t1 t.toCharArray() t.toCharArray t int suma=0; suma 0 for(int i=0;i<s.length();i++) {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		} int i=0; int i=0; i 0 i<s.length() i s.length() s.length s i++ i++ i {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		} {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		} if(s1[i]!=t1[i]) {
				suma++;
			} s1[i]!=t1[i] s1[i] s1 i t1[i] t1 i {
				suma++;
			} suma++ suma System.out.println(suma) System.out.println System.out System System.out suma String[] args args public class Main {

	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);// TODO Auto-generated method stub
		String s=input.next();
		String t=input.next();
		char[] s1=s.toCharArray();
		char[] t1=t.toCharArray();
		int suma=0;
		for(int i=0;i<s.length();i++) {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		}
		System.out.println(suma);
			
	}

} public class Main {

	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);// TODO Auto-generated method stub
		String s=input.next();
		String t=input.next();
		char[] s1=s.toCharArray();
		char[] t1=t.toCharArray();
		int suma=0;
		for(int i=0;i<s.length();i++) {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		}
		System.out.println(suma);
			
	}

} Main
import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);// TODO Auto-generated method stub
		String s=input.next();
		String t=input.next();
		char[] s1=s.toCharArray();
		char[] t1=t.toCharArray();
		int suma=0;
		for(int i=0;i<s.length();i++) {
			if(s1[i]!=t1[i]) {
				suma++;
			}
		}
		System.out.println(suma);
			
	}

}
