import java.io.*;

public class Main{
	private static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	private static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
	
	public static void main (String[] args) throws IOException{
        String s = br.readLine();
        String t = br.readLine();
        int ans = 0;
        for(int i=0;i<s.length();i++){
            if(s.charAt(i)!=t.charAt(i))    ans++;
        }
        bw.write(ans + "");
		bw.flush();
	}
}

/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