import java.util.Scanner;

public class Main {
	
	public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		
		String[] a = scanner.next().split("");
		String[] b = scanner.next().split("");
		
		scanner.close();
		
		int result = 0;
		
		for (int i = 0; i < a.length; i++) {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		}
		
		System.out.println(result);
	}

} import java.util.Scanner; Scanner java.util public class Main {
	
	public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		
		String[] a = scanner.next().split("");
		String[] b = scanner.next().split("");
		
		scanner.close();
		
		int result = 0;
		
		for (int i = 0; i < a.length; i++) {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		}
		
		System.out.println(result);
	}

} Main public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		
		String[] a = scanner.next().split("");
		String[] b = scanner.next().split("");
		
		scanner.close();
		
		int result = 0;
		
		for (int i = 0; i < a.length; i++) {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		}
		
		System.out.println(result);
	} main {
		
		Scanner scanner = new Scanner(System.in);
		
		String[] a = scanner.next().split("");
		String[] b = scanner.next().split("");
		
		scanner.close();
		
		int result = 0;
		
		for (int i = 0; i < a.length; i++) {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		}
		
		System.out.println(result);
	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) String[] a = scanner.next().split(""); a scanner.next().split("") scanner.next().split scanner.next() scanner.next scanner "" String[] b = scanner.next().split(""); b scanner.next().split("") scanner.next().split scanner.next() scanner.next scanner "" scanner.close() scanner.close scanner int result = 0; result 0 for (int i = 0; i < a.length; i++) {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		} int i = 0; int i = 0; i 0 i < a.length i a.length a a.length i++ i++ i {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		} {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		} if (a[i].equals(b[i])) {
				
			} else {
				result++;
			} a[i].equals(b[i]) a[i].equals a[i] a i b[i] b i {
				
			} {
				result++;
			} result++ result System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main {
	
	public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		
		String[] a = scanner.next().split("");
		String[] b = scanner.next().split("");
		
		scanner.close();
		
		int result = 0;
		
		for (int i = 0; i < a.length; i++) {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		}
		
		System.out.println(result);
	}

} public class Main {
	
	public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		
		String[] a = scanner.next().split("");
		String[] b = scanner.next().split("");
		
		scanner.close();
		
		int result = 0;
		
		for (int i = 0; i < a.length; i++) {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		}
		
		System.out.println(result);
	}

} Main
import java.util.Scanner;

public class Main {
	
	public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		
		String[] a = scanner.next().split("");
		String[] b = scanner.next().split("");
		
		scanner.close();
		
		int result = 0;
		
		for (int i = 0; i < a.length; i++) {
			
			if (a[i].equals(b[i])) {
				
			} else {
				result++;
			}
		}
		
		System.out.println(result);
	}

}
