#include<bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
typedef long long ll;
typedef pair<int,int> P;
int main()
{
    vector<int> A(4);
    rep(i, 4) cin >> A[i];
    sort(A.begin(), A.end());
    rep(i,3){
        if(A.at(i)+1!=A.at(i+1)){
            cout << "No" << endl;
            return 0;
        }
    
    }
    cout << "Yes" << endl;
}