/* -*- coding: utf-8 -*-
 *
 * 998.cc:  No.998 Four Integers - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int N = 4;

/* typedef */

/* global variables */

int as[N];

/* subroutines */

/* main */

int main() {
  for (int i = 0; i < N; i++) scanf("%d", as + i);
  sort(as, as + N);

  for (int i = 0; i + 1 < N; i++)
    if (as[i] + 1 != as[i + 1]) {
      puts("No");
      return 0;
    }

  puts("Yes");
  return 0;
}