#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <utility>
#include <vector>
#include <stack>

using namespace std;
#define rep(i, n) for (int i = 0; i < n; i++)
#define rep1(i, n) for (int i = 1; i < n + 1; i++)
#define all(A) A.begin(), A.end()
#define itr(A, l, r) A.begin() + l, A.begin() + r
#define debug(var) cout << #var << " = " << var << endl;
typedef long long ll;

int main(void)
{
    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])
    {
        cout << "Yes" << endl;
    }
    else
    {
        cout << "No" << endl;
    }
}