import java.io.*;
import java.util.*;

public class Main {
    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    private static final PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    private static StringTokenizer st;

    private static String readToken() throws IOException {
        while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(br.readLine());
        return st.nextToken();
    }

    public static void main(String[] args) throws IOException {
        char[] S = readToken().toCharArray();
        char[] T = readToken().toCharArray();

        int count = 0;
        for (int i = 0; i < S.length; i++) {
            if (S[i] != T[i]) count++;
        }
        pw.println(count);
        pw.close();
    }
} import java.io.*; io.* java import java.util.*; util.* java public class Main {
    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    private static final PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    private static StringTokenizer st;

    private static String readToken() throws IOException {
        while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(br.readLine());
        return st.nextToken();
    }

    public static void main(String[] args) throws IOException {
        char[] S = readToken().toCharArray();
        char[] T = readToken().toCharArray();

        int count = 0;
        for (int i = 0; i < S.length; i++) {
            if (S[i] != T[i]) count++;
        }
        pw.println(count);
        pw.close();
    }
} Main private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) private static final PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out))); pw new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out))) private static StringTokenizer st; st private static String readToken() throws IOException {
        while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(br.readLine());
        return st.nextToken();
    } readToken {
        while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(br.readLine());
        return st.nextToken();
    } while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(br.readLine()); st == null || !st.hasMoreTokens() st == null st null !st.hasMoreTokens() st.hasMoreTokens() st.hasMoreTokens st st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st public static void main(String[] args) throws IOException {
        char[] S = readToken().toCharArray();
        char[] T = readToken().toCharArray();

        int count = 0;
        for (int i = 0; i < S.length; i++) {
            if (S[i] != T[i]) count++;
        }
        pw.println(count);
        pw.close();
    } main {
        char[] S = readToken().toCharArray();
        char[] T = readToken().toCharArray();

        int count = 0;
        for (int i = 0; i < S.length; i++) {
            if (S[i] != T[i]) count++;
        }
        pw.println(count);
        pw.close();
    } char[] S = readToken().toCharArray(); S readToken().toCharArray() readToken().toCharArray readToken() readToken char[] T = readToken().toCharArray(); T readToken().toCharArray() readToken().toCharArray readToken() readToken int count = 0; count 0 for (int i = 0; i < S.length; i++) {
            if (S[i] != T[i]) count++;
        } 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]) count++;
        } {
            if (S[i] != T[i]) count++;
        } if (S[i] != T[i]) count++; S[i] != T[i] S[i] S i T[i] T i count++ count pw.println(count) pw.println pw count pw.close() pw.close pw String[] args args public class Main {
    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    private static final PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    private static StringTokenizer st;

    private static String readToken() throws IOException {
        while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(br.readLine());
        return st.nextToken();
    }

    public static void main(String[] args) throws IOException {
        char[] S = readToken().toCharArray();
        char[] T = readToken().toCharArray();

        int count = 0;
        for (int i = 0; i < S.length; i++) {
            if (S[i] != T[i]) count++;
        }
        pw.println(count);
        pw.close();
    }
} public class Main {
    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    private static final PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    private static StringTokenizer st;

    private static String readToken() throws IOException {
        while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(br.readLine());
        return st.nextToken();
    }

    public static void main(String[] args) throws IOException {
        char[] S = readToken().toCharArray();
        char[] T = readToken().toCharArray();

        int count = 0;
        for (int i = 0; i < S.length; i++) {
            if (S[i] != T[i]) count++;
        }
        pw.println(count);
        pw.close();
    }
} Main
import java.io.*;
import java.util.*;

public class Main {
    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    private static final PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    private static StringTokenizer st;

    private static String readToken() throws IOException {
        while (st == null || !st.hasMoreTokens()) st = new StringTokenizer(br.readLine());
        return st.nextToken();
    }

    public static void main(String[] args) throws IOException {
        char[] S = readToken().toCharArray();
        char[] T = readToken().toCharArray();

        int count = 0;
        for (int i = 0; i < S.length; i++) {
            if (S[i] != T[i]) count++;
        }
        pw.println(count);
        pw.close();
    }
}
