import java.util.*;

class Main{
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int diff = 0;
		
		String[] ss = s.split("");
		String[] tt = t.split("");
		
		for(int i=0;i<ss.length;i++) {
			if(ss[i].equals(tt[i])) {
			}else {
				diff++;
			}
		}
		
		System.out.println(diff);

	}
}
/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