#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<(n); ++i)
using ll = long long;

int main(){
    vector<int> a(4);
    rep(i,4) cin >> a[i];
    sort(a.begin(),a.end());
    for(int i=1; i<4; i++){
        if(a[i]!=a[i-1]+1){
            cout << "No" << endl;
            return 0;
        }
    }

    cout << "Yes" << endl;
}