#include <iostream>
#include <vector>
#include <algorithm>
#define rep(i, a, n) for(int i = a; i < n; i++)
using namespace std;

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