import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String S = sc.next();
        ArrayList<String> l = new ArrayList<>();
        int diffCnt = 0;
        int cnt = 0;
        for (int i = 0; i < S.length(); i++) {
            l.add(String.valueOf(S.charAt(i)));
        }
        Collections.sort(l);

        for (int i = 0; i < l.size() - 1; i++) {
            if (l.get(i).equals(l.get(i + 1))) {
                diffCnt++;
            }
        }

        System.out.println(diffCnt == 2 ? "Yes" : "No");
    }

}

/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