import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		String s = scanner.next();
		String t = scanner.next();
		int ans = solve(s.toCharArray(), t.toCharArray());
		System.out.println(ans);
	}

	public static int solve(char[] s, char[] t) {
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		}
		return ans;
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		String s = scanner.next();
		String t = scanner.next();
		int ans = solve(s.toCharArray(), t.toCharArray());
		System.out.println(ans);
	}

	public static int solve(char[] s, char[] t) {
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		}
		return ans;
	}
} Main public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		String s = scanner.next();
		String t = scanner.next();
		int ans = solve(s.toCharArray(), t.toCharArray());
		System.out.println(ans);
	} main {
		Scanner scanner = new Scanner(System.in);
		String s = scanner.next();
		String t = scanner.next();
		int ans = solve(s.toCharArray(), t.toCharArray());
		System.out.println(ans);
	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) String s = scanner.next(); s scanner.next() scanner.next scanner String t = scanner.next(); t scanner.next() scanner.next scanner int ans = solve(s.toCharArray(), t.toCharArray()); ans solve(s.toCharArray(), t.toCharArray()) solve s.toCharArray() s.toCharArray s t.toCharArray() t.toCharArray t System.out.println(ans) System.out.println System.out System System.out ans String[] args args public static int solve(char[] s, char[] t) {
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		}
		return ans;
	} solve {
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		}
		return ans;
	} int ans = 0; ans 0 for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		} int i = 0; int i = 0; i 0 i < s.length i s.length s s.length i++ i++ i {
			if (s[i] != t[i]) {
				ans++;
			}
		} {
			if (s[i] != t[i]) {
				ans++;
			}
		} if (s[i] != t[i]) {
				ans++;
			} s[i] != t[i] s[i] s i t[i] t i {
				ans++;
			} ans++ ans return ans; ans char[] s s char[] t t public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		String s = scanner.next();
		String t = scanner.next();
		int ans = solve(s.toCharArray(), t.toCharArray());
		System.out.println(ans);
	}

	public static int solve(char[] s, char[] t) {
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		}
		return ans;
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		String s = scanner.next();
		String t = scanner.next();
		int ans = solve(s.toCharArray(), t.toCharArray());
		System.out.println(ans);
	}

	public static int solve(char[] s, char[] t) {
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		}
		return ans;
	}
} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		String s = scanner.next();
		String t = scanner.next();
		int ans = solve(s.toCharArray(), t.toCharArray());
		System.out.println(ans);
	}

	public static int solve(char[] s, char[] t) {
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		}
		return ans;
	}
}
