#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
    vector<int> A(4);
    for(int i = 0; 4 > i; i++)cin>>A[i];
    sort(A.begin(),A.end());
    for(int i = 1; 4 > i; i++){
        if(A[i-1]+1 != A[i]){
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
}