import java.awt.*;
import java.util.*;
import java.io.*;
import java.math.BigDecimal;
import java.nio.file.Files;
import java.nio.charset.StandardCharsets;
//给出两个数a,b 求出[a,b]中各位数字之和能整除原数的数的个数。
public class Main {
    int mod  = (int) 1e9+7;
    //int n = (int) 1e6+5;
    //long[][] memo = new long[n][27];
    void solve(String s1, String s2) {
        char[] cs1 = s1.toCharArray();
        char[] cs2 = s2.toCharArray();
        int n = s1.length();
        int cnt = 0;
        for(int i=0;i<n;i++){
            if(cs1[i]!=cs2[i])cnt++;
        }
        System.out.println(cnt);
    } 
    //0 1 2 3 4 5 6 7
    //1 7 3 4 7 6 2 9
    //1 7 4 3 7 6 2 9;
    //1 2 1 2 1
    public static void main(String[] args)  throws IOException {
        // Use the Scanner class

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //String[]  s = br.readLine().split(" ");
        Main test = new Main();

        String s = br.readLine();
        String s2 = br.readLine();
        test.solve(s,s2);
    }
} import java.awt.*; awt.* java import java.util.*; util.* java import java.io.*; io.* java import java.math.BigDecimal; BigDecimal java.math import java.nio.file.Files; Files java.nio.file import java.nio.charset.StandardCharsets; StandardCharsets java.nio.charset public class Main {
    int mod  = (int) 1e9+7;
    //int n = (int) 1e6+5;
    //long[][] memo = new long[n][27];
    void solve(String s1, String s2) {
        char[] cs1 = s1.toCharArray();
        char[] cs2 = s2.toCharArray();
        int n = s1.length();
        int cnt = 0;
        for(int i=0;i<n;i++){
            if(cs1[i]!=cs2[i])cnt++;
        }
        System.out.println(cnt);
    } 
    //0 1 2 3 4 5 6 7
    //1 7 3 4 7 6 2 9
    //1 7 4 3 7 6 2 9;
    //1 2 1 2 1
    public static void main(String[] args)  throws IOException {
        // Use the Scanner class

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //String[]  s = br.readLine().split(" ");
        Main test = new Main();

        String s = br.readLine();
        String s2 = br.readLine();
        test.solve(s,s2);
    }
} Main int mod  = (int) 1e9+7; mod (int) 1e9+7 (int) 1e9 7 //int n = (int) 1e6+5;
    //long[][] memo = new long[n][27];
    void solve(String s1, String s2) {
        char[] cs1 = s1.toCharArray();
        char[] cs2 = s2.toCharArray();
        int n = s1.length();
        int cnt = 0;
        for(int i=0;i<n;i++){
            if(cs1[i]!=cs2[i])cnt++;
        }
        System.out.println(cnt);
    } solve {
        char[] cs1 = s1.toCharArray();
        char[] cs2 = s2.toCharArray();
        int n = s1.length();
        int cnt = 0;
        for(int i=0;i<n;i++){
            if(cs1[i]!=cs2[i])cnt++;
        }
        System.out.println(cnt);
    } char[] cs1 = s1.toCharArray(); cs1 s1.toCharArray() s1.toCharArray s1 char[] cs2 = s2.toCharArray(); cs2 s2.toCharArray() s2.toCharArray s2 int n = s1.length(); n s1.length() s1.length s1 int cnt = 0; cnt 0 for(int i=0;i<n;i++){
            if(cs1[i]!=cs2[i])cnt++;
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            if(cs1[i]!=cs2[i])cnt++;
        } {
            if(cs1[i]!=cs2[i])cnt++;
        } if(cs1[i]!=cs2[i])cnt++; cs1[i]!=cs2[i] cs1[i] cs1 i cs2[i] cs2 i cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String s1 s1 String s2 s2 //0 1 2 3 4 5 6 7
    //1 7 3 4 7 6 2 9
    //1 7 4 3 7 6 2 9;
    //1 2 1 2 1
    public static void main(String[] args)  throws IOException {
        // Use the Scanner class

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //String[]  s = br.readLine().split(" ");
        Main test = new Main();

        String s = br.readLine();
        String s2 = br.readLine();
        test.solve(s,s2);
    } main {
        // Use the Scanner class

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //String[]  s = br.readLine().split(" ");
        Main test = new Main();

        String s = br.readLine();
        String s2 = br.readLine();
        test.solve(s,s2);
    } BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) Main test = new Main(); test new Main() String s = br.readLine(); s br.readLine() br.readLine br String s2 = br.readLine(); s2 br.readLine() br.readLine br test.solve(s,s2) test.solve test s s2 String[] args args public class Main {
    int mod  = (int) 1e9+7;
    //int n = (int) 1e6+5;
    //long[][] memo = new long[n][27];
    void solve(String s1, String s2) {
        char[] cs1 = s1.toCharArray();
        char[] cs2 = s2.toCharArray();
        int n = s1.length();
        int cnt = 0;
        for(int i=0;i<n;i++){
            if(cs1[i]!=cs2[i])cnt++;
        }
        System.out.println(cnt);
    } 
    //0 1 2 3 4 5 6 7
    //1 7 3 4 7 6 2 9
    //1 7 4 3 7 6 2 9;
    //1 2 1 2 1
    public static void main(String[] args)  throws IOException {
        // Use the Scanner class

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //String[]  s = br.readLine().split(" ");
        Main test = new Main();

        String s = br.readLine();
        String s2 = br.readLine();
        test.solve(s,s2);
    }
} public class Main {
    int mod  = (int) 1e9+7;
    //int n = (int) 1e6+5;
    //long[][] memo = new long[n][27];
    void solve(String s1, String s2) {
        char[] cs1 = s1.toCharArray();
        char[] cs2 = s2.toCharArray();
        int n = s1.length();
        int cnt = 0;
        for(int i=0;i<n;i++){
            if(cs1[i]!=cs2[i])cnt++;
        }
        System.out.println(cnt);
    } 
    //0 1 2 3 4 5 6 7
    //1 7 3 4 7 6 2 9
    //1 7 4 3 7 6 2 9;
    //1 2 1 2 1
    public static void main(String[] args)  throws IOException {
        // Use the Scanner class

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //String[]  s = br.readLine().split(" ");
        Main test = new Main();

        String s = br.readLine();
        String s2 = br.readLine();
        test.solve(s,s2);
    }
} Main
import java.awt.*;
import java.util.*;
import java.io.*;
import java.math.BigDecimal;
import java.nio.file.Files;
import java.nio.charset.StandardCharsets;
//给出两个数a,b 求出[a,b]中各位数字之和能整除原数的数的个数。
public class Main {
    int mod  = (int) 1e9+7;
    //int n = (int) 1e6+5;
    //long[][] memo = new long[n][27];
    void solve(String s1, String s2) {
        char[] cs1 = s1.toCharArray();
        char[] cs2 = s2.toCharArray();
        int n = s1.length();
        int cnt = 0;
        for(int i=0;i<n;i++){
            if(cs1[i]!=cs2[i])cnt++;
        }
        System.out.println(cnt);
    } 
    //0 1 2 3 4 5 6 7
    //1 7 3 4 7 6 2 9
    //1 7 4 3 7 6 2 9;
    //1 2 1 2 1
    public static void main(String[] args)  throws IOException {
        // Use the Scanner class

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //String[]  s = br.readLine().split(" ");
        Main test = new Main();

        String s = br.readLine();
        String s2 = br.readLine();
        test.solve(s,s2);
    }
}
