#include <bits/stdc++.h>
using namespace std;

int main(){
    vector<int> key(4, 0);
    for(int i = 0; i < 4; i++) cin >> key.at(i);
    sort(key.begin(), key.end());
    string ans = "Yes";
    for(int i = 0; i < 3; i++){
        if(key.at(i) + 1 != key.at(i+1)) ans = "No";
    }
    cout << ans << endl;
}