#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;

#define MOD 1000000007

int main() {
  vector<int> a(4);
  for (int i = 0; i < 4; ++i) {
    cin >> a[i];
  }
  sort(a.begin(), a.end());
  for (int i = 0; i + 1 < 4; ++i) {
    if (a[i] + 1 != a[i + 1]) {
      cout << "No" << endl;
      return 0;
    }
  }
  cout << "Yes" << endl;
  return 0;
}