#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<n; i++)
#define Sort(vector) sort(vector.begin(), vector.end())
#define Reverse(vector) reverse(vector.begin(), vector.end())
#define RSort(vector) sort(vector.rbegin(), vector.rend())
using ll = long long;
using P = pair<int,int>;
using TU = tuple<int,int,int>;
using vint = vector<int>;
using vvint = vector<vint>;
using vvvint = vector<vvint>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
template<typename T> istream &operator>>(istream &is,vector<T> &v){for(T &in:v){is>>in;}return is;}
template<typename T> ostream &operator<<(ostream &os,vector<T> &v){for(int i=0;i<(int)v.size();i++){os<<v[i]<<" \n"[i==(int)v.size()-1];}return os;}
template<typename T> istream &operator>>(istream &is,vector<vector<T>> &v){for(vector<T> &in:v){is>>in;}return is;}
template<typename T> ostream &operator<<(ostream &os,vector<vector<T>> &v){for(vector<T> &out:v){os<<out;}return os;}




int main(){
  string s;cin>>s;

  set<int> st;
  for(auto c:s){
    st.insert(c);
  }
  if(st.size()!=2) {
    cout << "No" << '\n';
    return 0;
  }

  if(s[0]==s[1]) cout << "Yes" << '\n';
  else cout << "No" << '\n';

  return 0;
}