#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,m,n) for(int i=m; i<n; ++i)
#define repl(i,m,n) for(ll i=m; i<n; ++i)

int main(){
    vector<int> A(4);
    for(int &a : A) cin >> a;

    sort(A.begin(), A.end());
    rep(i, 0, 3){
        if(A[i] + 1 != A[i+1]){
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;

    return 0;
}