#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define ALL(v) (v).begin(), (v).end()
#define coutd(n) cout << fixed << setprecision(n)
#define ll long long int
#define vl vector<ll>
#define vi vector<int>
const int INF = 2147483647;
const ll MOD = 1000000007;

using namespace std;

int main() {
  vi a(4);
  REP(i, 4) { cin >> a[i]; }
  sort(ALL(a));
  if (a[0] + 1 == a[1] && a[1] + 1 == a[2] && a[3] + 1 == a[4]) {
    cout << "Yes" << endl;
  } else {
    cout << "No" << endl;
  }
  return 0;
}