        import java.util.Scanner;
        public class Main {
        	 public static void main(String args[]){
        	Scanner scanner = new Scanner(System.in);
        	
        	String a=scanner.next();
        	String b=scanner.next();
               int n=0;
        	// 変数strの長さ分回す
        	for (int i = 0; i < a.length(); i++) {
        	    // strの先頭から1文字ずつString型にして取り出す
        	    String str1 = String.valueOf(a.charAt(i));
        	    String str2 = String.valueOf(b.charAt(i));
        	    if(!(str1.equals(str2))){
        	    	n=n+1;
                }}
        	   System.out.println(n);
         
        	}
        }
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz