import java.util.Arrays;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Vector;

//1, 12, 123, 1234
public class Main {
	public static void main(String args[]) {
		Scanner in = new Scanner(System.in);
		String s = in.next();
		String t = in.next();
		int count = 0;
		for (int i = 0; i <s.length(); i++) {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		}
		System.out.println(count);
	}
} import java.util.Arrays; Arrays java.util import java.util.HashSet; HashSet java.util import java.util.Scanner; Scanner java.util import java.util.Vector; Vector java.util public class Main {
	public static void main(String args[]) {
		Scanner in = new Scanner(System.in);
		String s = in.next();
		String t = in.next();
		int count = 0;
		for (int i = 0; i <s.length(); i++) {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		}
		System.out.println(count);
	}
} Main public static void main(String args[]) {
		Scanner in = new Scanner(System.in);
		String s = in.next();
		String t = in.next();
		int count = 0;
		for (int i = 0; i <s.length(); i++) {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		}
		System.out.println(count);
	} main {
		Scanner in = new Scanner(System.in);
		String s = in.next();
		String t = in.next();
		int count = 0;
		for (int i = 0; i <s.length(); i++) {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		}
		System.out.println(count);
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) String s = in.next(); s in.next() in.next in String t = in.next(); t in.next() in.next in int count = 0; count 0 for (int i = 0; i <s.length(); i++) {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		} 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)) {
				count++;
			}
		} {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		} if (s.charAt(i)!=t.charAt(i)) {
				count++;
			} s.charAt(i)!=t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i {
				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 in = new Scanner(System.in);
		String s = in.next();
		String t = in.next();
		int count = 0;
		for (int i = 0; i <s.length(); i++) {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		}
		System.out.println(count);
	}
} public class Main {
	public static void main(String args[]) {
		Scanner in = new Scanner(System.in);
		String s = in.next();
		String t = in.next();
		int count = 0;
		for (int i = 0; i <s.length(); i++) {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		}
		System.out.println(count);
	}
} Main
import java.util.Arrays;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Vector;

//1, 12, 123, 1234
public class Main {
	public static void main(String args[]) {
		Scanner in = new Scanner(System.in);
		String s = in.next();
		String t = in.next();
		int count = 0;
		for (int i = 0; i <s.length(); i++) {
			if (s.charAt(i)!=t.charAt(i)) {
				count++;
			}
		}
		System.out.println(count);
	}
}