#include <bits/stdc++.h>
using namespace std;
#define ALL(a) (a).begin(),(a).end()
#define rALL(a) (a).rbegin(),(a).rend()
typedef pair<int, int> Pint;
typedef pair<int64_t, int64_t> Pll;

int main() {
    vector<int> A(4);
    for (int i = 0; i < 4; i++){
        cin >> A.at(i);
    }
    sort(ALL(A));
    for (int i = 0; i < 3; i++){
        if (A.at(i) + 1 != A.at(i + 1)){
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
}