#include<bits/stdc++.h>
using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string s;
  cin >> s;
  bool flg = true;
  set<char> st;
  for (int i = 0; i < s.size(); i++) {
    if (!isalpha(s[i])) flg = false;
    st.emplace(s[i]);
  }

  if (s[0] == s[1] && st.size() == 2) cout << "Yes" << endl;
  else cout << "No" << endl;
  return 0;
}