#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
    vector<int> V(4);
    for(int i=0; i<4; i++) cin >> V[i];
    sort(V.begin(), V.end());

    bool ok = true;
    for(size_t i=0; i+1<4; i++) ok &= (V[i] + 1 == V[i+1]);
    cout << (ok ? "Yes" : "No") << endl;
    return 0;
}