import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;
public class Main {
	public static void main(String[] args)throws IOException {
		FastReader sc = new FastReader();
		PrintWriter pw = new PrintWriter(System.out);
		String s = sc.next();
		String t = sc.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count++;
		}
		System.out.println(count);

	}
}





class FastReader {
	BufferedReader br;
	StringTokenizer st;

	public FastReader() {
		br = new BufferedReader(new
		                        InputStreamReader(System.in));
	}

	String next() {
		while (st == null || !st.hasMoreElements()) {
			try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException  e) {
				e.printStackTrace();
			}
		}
		return st.nextToken();
	}

	int nextInt() {
		return Integer.parseInt(next());
	}

	long nextLong() {
		return Long.parseLong(next());
	}

	double nextDouble() {
		return Double.parseDouble(next());
	}

	String nextLine() {
		String str = "";
		try {
			str = br.readLine();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return str;
	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.PrintWriter; PrintWriter java.io import java.util.*; util.* java public class Main {
	public static void main(String[] args)throws IOException {
		FastReader sc = new FastReader();
		PrintWriter pw = new PrintWriter(System.out);
		String s = sc.next();
		String t = sc.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)throws IOException {
		FastReader sc = new FastReader();
		PrintWriter pw = new PrintWriter(System.out);
		String s = sc.next();
		String t = sc.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 {
		FastReader sc = new FastReader();
		PrintWriter pw = new PrintWriter(System.out);
		String s = sc.next();
		String t = sc.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count++;
		}
		System.out.println(count);

	} FastReader sc = new FastReader(); sc new FastReader() PrintWriter pw = new PrintWriter(System.out); pw new PrintWriter(System.out) String s = sc.next(); s sc.next() sc.next sc String t = sc.next(); t sc.next() sc.next sc 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 System.out.println(count) System.out.println System.out System System.out count String[] args args class FastReader {
	BufferedReader br;
	StringTokenizer st;

	public FastReader() {
		br = new BufferedReader(new
		                        InputStreamReader(System.in));
	}

	String next() {
		while (st == null || !st.hasMoreElements()) {
			try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException  e) {
				e.printStackTrace();
			}
		}
		return st.nextToken();
	}

	int nextInt() {
		return Integer.parseInt(next());
	}

	long nextLong() {
		return Long.parseLong(next());
	}

	double nextDouble() {
		return Double.parseDouble(next());
	}

	String nextLine() {
		String str = "";
		try {
			str = br.readLine();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return str;
	}
} FastReader BufferedReader br; br StringTokenizer st; st public FastReader() {
		br = new BufferedReader(new
		                        InputStreamReader(System.in));
	} FastReader {
		br = new BufferedReader(new
		                        InputStreamReader(System.in));
	} br = new BufferedReader(new
		                        InputStreamReader(System.in)) br new BufferedReader(new
		                        InputStreamReader(System.in)) String next() {
		while (st == null || !st.hasMoreElements()) {
			try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException  e) {
				e.printStackTrace();
			}
		}
		return st.nextToken();
	} next {
		while (st == null || !st.hasMoreElements()) {
			try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException  e) {
				e.printStackTrace();
			}
		}
		return st.nextToken();
	} while (st == null || !st.hasMoreElements()) {
			try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException  e) {
				e.printStackTrace();
			}
		} st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
			try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException  e) {
				e.printStackTrace();
			}
		} try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException  e) {
				e.printStackTrace();
			} catch (IOException  e) {
				e.printStackTrace();
			} IOException  e {
				e.printStackTrace();
			} e.printStackTrace() e.printStackTrace e {
				st = new StringTokenizer(br.readLine());
			} st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {
		return Integer.parseInt(next());
	} nextInt {
		return Integer.parseInt(next());
	} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {
		return Long.parseLong(next());
	} nextLong {
		return Long.parseLong(next());
	} return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() {
		return Double.parseDouble(next());
	} nextDouble {
		return Double.parseDouble(next());
	} return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() {
		String str = "";
		try {
			str = br.readLine();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return str;
	} nextLine {
		String str = "";
		try {
			str = br.readLine();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return str;
	} String str = ""; str "" try {
			str = br.readLine();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} IOException e {
			e.printStackTrace();
		} e.printStackTrace() e.printStackTrace e {
			str = br.readLine();
		} str = br.readLine() str br.readLine() br.readLine br return str; str public class Main {
	public static void main(String[] args)throws IOException {
		FastReader sc = new FastReader();
		PrintWriter pw = new PrintWriter(System.out);
		String s = sc.next();
		String t = sc.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)throws IOException {
		FastReader sc = new FastReader();
		PrintWriter pw = new PrintWriter(System.out);
		String s = sc.next();
		String t = sc.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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;
public class Main {
	public static void main(String[] args)throws IOException {
		FastReader sc = new FastReader();
		PrintWriter pw = new PrintWriter(System.out);
		String s = sc.next();
		String t = sc.next();
		int count = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i))
				count++;
		}
		System.out.println(count);

	}
}





class FastReader {
	BufferedReader br;
	StringTokenizer st;

	public FastReader() {
		br = new BufferedReader(new
		                        InputStreamReader(System.in));
	}

	String next() {
		while (st == null || !st.hasMoreElements()) {
			try {
				st = new StringTokenizer(br.readLine());
			} catch (IOException  e) {
				e.printStackTrace();
			}
		}
		return st.nextToken();
	}

	int nextInt() {
		return Integer.parseInt(next());
	}

	long nextLong() {
		return Long.parseLong(next());
	}

	double nextDouble() {
		return Double.parseDouble(next());
	}

	String nextLine() {
		String str = "";
		try {
			str = br.readLine();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return str;
	}
}