#include <bits/stdc++.h>
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
using namespace std;
const long long MOD = 1000000007LL, INF = 1e9, LINF = 1e18;
const long double PI = 3.141592653589793116, EPS = 1e-9,
                  GOLD = ((1 + sqrt(5)) / 2);
template <class T>
int getbit(T s, int i) {
  return (s >> 1) & 1;
}
template <class T>
T onbit(T s, int i) {
  return s | (T(1) << i);
}
template <class T>
T offbit(T s, int i) {
  return s & (~(T(1) << i));
}
template <class T>
int cntbit(T s) {
  return __builtin_popcount(s);
}
string s;
long long n;
vector<long long> cc(26, 0);
void VarInput() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cin >> s;
  n = s.size();
}
void ProSolve() {
  for (long long i = 0; i < n; i++) cc[s[i] - 'a']++;
  long long appear = 0, onlyOne = 0;
  for (long long i = 0; i < 26; i++) {
    if (cc[i] > 0) appear++;
    if (cc[i] == 1) onlyOne++;
  }
  if (appear > 4) {
    cout << "No";
    return;
  }
  if (appear < 2) {
    cout << "No";
    return;
  }
  if (appear == 2 && onlyOne > 0) {
    cout << "No";
    return;
  }
  if (appear == 3 && onlyOne > 2) {
    cout << "No";
    return;
  }
  cout << "Yes";
}
int main() {
  VarInput();
  ProSolve();
}
