#include <bits/stdc++.h>
#define rep(i,n) for (ll i = 0; i < n; ++i)
#define sz(x) int(x.size())
#define ALL(c) (c).begin(), (c).end()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v, x) (std::find(v.begin(), v.end(), x) != v.end())
#define FORV(i, v) for (auto i = v.begin(); i != v.end(); i++)
using namespace std;

typedef long long ll;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
const int INF = 1001001001;
const long long INFL = (1LL<<60);
const double eps = (1e-9);

ll calc(ll x) {
  ll ret = 0;
  while (x != 0) {
    ret += x % 10;
    x /= 10;
  }
  return ret;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  vector<int> a(4);
  rep(i, 4) cin >> a[i];

  sort(ALL(a));
  if (a[0] +1 == a[1] && a[1] + 1 == a[2] && a[2] + 1 == a[3]) {
    puts("Yes");
  } else {
    puts("No");
  }

  return 0;
}