text: #include <bits/stdc++.h>
  #define rep(i, n) for (int i = 0; i < (n); ++i)
  using namespace std;
  using ll = long long;
  using P = pair<int, int>;
  
  int main() {
    string s;
    cin >> s;
    map<char, int> mp;
    rep(i, s.size()) mp[s[i]]++;
    if (mp.size() != 2) {
      cout << "No" << endl;
      return 0;
    }
    for (auto p : mp) {
      if (p.second != 2) {
        cout << "No" << endl;
        return 0;
      }
    }
    cout << "Yes" << endl;
    return 0;
  }