import java.util.Scanner;
public class Main{
	public static void main(String[] args){
		Scanner s = new Scanner(System.in);
		
		String ss = s.nextLine();
		String st = s.nextLine();
		
		int count=0;
		
		char[] sstri= ss.toCharArray();
		char[] tstri= st.toCharArray();
		
		for(int i=0;i<sstri.length;i++){
			if(sstri[i] != tstri[i]){
				count++;
			}
		}
		System.out.print(count);
	}
}
/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