#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;

int main(){
    int a, b, c, d;
    vector<int> l(4);
    for (int i = 0; i < 4; i++) cin >> l[i];
    sort(l.begin(), l.end());
    for (int i = 0; i < 3; i++){
        if (l[i] + 1 != l[i+1]){
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
}