import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        }catch(Exception e){
            System.out.println(e);
        }
    }
} import java.io.*; io.* java public class Main {
    public static void main(String[] args) throws Exception {
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        }catch(Exception e){
            System.out.println(e);
        }
    }
} Main public static void main(String[] args) throws Exception {
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        }catch(Exception e){
            System.out.println(e);
        }
    } main {
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        }catch(Exception e){
            System.out.println(e);
        }
    } try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        }catch(Exception e){
            System.out.println(e);
        } catch(Exception e){
            System.out.println(e);
        } Exception e {
            System.out.println(e);
        } System.out.println(e) System.out.println System.out System System.out e {
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        } BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) String S = br.readLine(); S br.readLine() br.readLine br String T = br.readLine(); T br.readLine() br.readLine br char charS[] = S.toCharArray(); charS S.toCharArray() S.toCharArray S char charT[] = T.toCharArray(); charT T.toCharArray() T.toCharArray T int ans = 0; ans 0 for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            } int i=0; int i=0; i 0 i<S.length() i S.length() S.length S i++ i++ i {
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            } {
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            } if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                } charS[i] != charT[i] charS[i] charS i charT[i] charT i {
                    charS[i] = charT[i];
                    ans++;
                } charS[i] = charT[i] charS[i] charS i charT[i] charT i ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        }catch(Exception e){
            System.out.println(e);
        }
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        }catch(Exception e){
            System.out.println(e);
        }
    }
} Main
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String S = br.readLine();
            String T = br.readLine();
            char charS[] = S.toCharArray();
            char charT[] = T.toCharArray();
            
            int ans = 0;
            for(int i=0; i<S.length(); i++){
                if(charS[i] != charT[i]){
                    charS[i] = charT[i];
                    ans++;
                }
            }
            
            System.out.println(ans);
            
        }catch(Exception e){
            System.out.println(e);
        }
    }
}