#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n); i++)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
using P = pair<int, int>;
const int INF = 1e9;
const long long LINF = 1e18;
const long long MOD = 1e9 + 7;

signed main(){
    int a[4];
    cin >> a[0] >> a[1] >> a[2] >> a[3];
    sort(a, a + 4);
    rep(i,3){
        if(a[i] + 1 != a[i + 1]){
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
    return 0;
}