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();
		char[] sa = s.toCharArray();
		char[] ta = t.toCharArray();
		int count = 0;
		for (int i = 0; i < sa.length; i++) {
			if (sa[i] != ta[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();
		char[] sa = s.toCharArray();
		char[] ta = t.toCharArray();
		int count = 0;
		for (int i = 0; i < sa.length; i++) {
			if (sa[i] != ta[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();
		char[] sa = s.toCharArray();
		char[] ta = t.toCharArray();
		int count = 0;
		for (int i = 0; i < sa.length; i++) {
			if (sa[i] != ta[i]) {
				count++;
			}
		}
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);

		String s = sc.next();
		String t = sc.next();
		char[] sa = s.toCharArray();
		char[] ta = t.toCharArray();
		int count = 0;
		for (int i = 0; i < sa.length; i++) {
			if (sa[i] != ta[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 char[] sa = s.toCharArray(); sa s.toCharArray() s.toCharArray s char[] ta = t.toCharArray(); ta t.toCharArray() t.toCharArray t int count = 0; count 0 for (int i = 0; i < sa.length; i++) {
			if (sa[i] != ta[i]) {
				count++;
			}
		} int i = 0; int i = 0; i 0 i < sa.length i sa.length sa sa.length i++ i++ i {
			if (sa[i] != ta[i]) {
				count++;
			}
		} {
			if (sa[i] != ta[i]) {
				count++;
			}
		} if (sa[i] != ta[i]) {
				count++;
			} sa[i] != ta[i] sa[i] sa i ta[i] ta 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 sc = new Scanner(System.in);

		String s = sc.next();
		String t = sc.next();
		char[] sa = s.toCharArray();
		char[] ta = t.toCharArray();
		int count = 0;
		for (int i = 0; i < sa.length; i++) {
			if (sa[i] != ta[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();
		char[] sa = s.toCharArray();
		char[] ta = t.toCharArray();
		int count = 0;
		for (int i = 0; i < sa.length; i++) {
			if (sa[i] != ta[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();
		char[] sa = s.toCharArray();
		char[] ta = t.toCharArray();
		int count = 0;
		for (int i = 0; i < sa.length; i++) {
			if (sa[i] != ta[i]) {
				count++;
			}
		}
		System.out.println(count);
	}
}