import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String S = sc.next();
		String T = sc.next();

		int ans = 0;
		for (int n=0; n<S.length(); n++) {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		}
		System.out.println(ans);
	}

	private static class FastScanner {
		private BufferedReader reader = null;
		private StringTokenizer tokenizer = null;

		public FastScanner(InputStream in) {
			reader = new BufferedReader(new InputStreamReader(in));
			tokenizer = null;
		}

		public String next() {
			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}

	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.StringTokenizer; StringTokenizer java.util public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String S = sc.next();
		String T = sc.next();

		int ans = 0;
		for (int n=0; n<S.length(); n++) {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		}
		System.out.println(ans);
	}

	private static class FastScanner {
		private BufferedReader reader = null;
		private StringTokenizer tokenizer = null;

		public FastScanner(InputStream in) {
			reader = new BufferedReader(new InputStreamReader(in));
			tokenizer = null;
		}

		public String next() {
			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}

	}
} Main public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String S = sc.next();
		String T = sc.next();

		int ans = 0;
		for (int n=0; n<S.length(); n++) {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		}
		System.out.println(ans);
	} main {
		FastScanner sc = new FastScanner(System.in);

		String S = sc.next();
		String T = sc.next();

		int ans = 0;
		for (int n=0; n<S.length(); n++) {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		}
		System.out.println(ans);
	} FastScanner sc = new FastScanner(System.in); sc new FastScanner(System.in) String S = sc.next(); S sc.next() sc.next sc String T = sc.next(); T sc.next() sc.next sc int ans = 0; ans 0 for (int n=0; n<S.length(); n++) {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		} int n=0; int n=0; n 0 n<S.length() n S.length() S.length S n++ n++ n {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		} {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		} if (S.charAt(n) != T.charAt(n)) {
				ans++;
			} S.charAt(n) != T.charAt(n) S.charAt(n) S.charAt S n T.charAt(n) T.charAt T n {
				ans++;
			} ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args private static class FastScanner {
		private BufferedReader reader = null;
		private StringTokenizer tokenizer = null;

		public FastScanner(InputStream in) {
			reader = new BufferedReader(new InputStreamReader(in));
			tokenizer = null;
		}

		public String next() {
			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}

	} FastScanner private BufferedReader reader = null; reader null private StringTokenizer tokenizer = null; tokenizer null public FastScanner(InputStream in) {
			reader = new BufferedReader(new InputStreamReader(in));
			tokenizer = null;
		} FastScanner {
			reader = new BufferedReader(new InputStreamReader(in));
			tokenizer = null;
		} reader = new BufferedReader(new InputStreamReader(in)) reader new BufferedReader(new InputStreamReader(in)) tokenizer = null tokenizer null InputStream in in public String next() {
			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		} next {
			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		} if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			} tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			} try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				} catch (IOException e) {
					throw new RuntimeException(e);
				} IOException e {
					throw new RuntimeException(e);
				} throw new RuntimeException(e); new RuntimeException(e) {
					tokenizer = new StringTokenizer(reader.readLine());
				} tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String S = sc.next();
		String T = sc.next();

		int ans = 0;
		for (int n=0; n<S.length(); n++) {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		}
		System.out.println(ans);
	}

	private static class FastScanner {
		private BufferedReader reader = null;
		private StringTokenizer tokenizer = null;

		public FastScanner(InputStream in) {
			reader = new BufferedReader(new InputStreamReader(in));
			tokenizer = null;
		}

		public String next() {
			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}

	}
} public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String S = sc.next();
		String T = sc.next();

		int ans = 0;
		for (int n=0; n<S.length(); n++) {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		}
		System.out.println(ans);
	}

	private static class FastScanner {
		private BufferedReader reader = null;
		private StringTokenizer tokenizer = null;

		public FastScanner(InputStream in) {
			reader = new BufferedReader(new InputStreamReader(in));
			tokenizer = null;
		}

		public String next() {
			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}

	}
} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String S = sc.next();
		String T = sc.next();

		int ans = 0;
		for (int n=0; n<S.length(); n++) {
			if (S.charAt(n) != T.charAt(n)) {
				ans++;
			}
		}
		System.out.println(ans);
	}

	private static class FastScanner {
		private BufferedReader reader = null;
		private StringTokenizer tokenizer = null;

		public FastScanner(InputStream in) {
			reader = new BufferedReader(new InputStreamReader(in));
			tokenizer = null;
		}

		public String next() {
			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}

	}
}
