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

int main() {
    vector<int> A(4);
    rep(i, 4) cin >> A[i];
    sort(A.begin(), A.end());
    string ans = "Yes\n";
    rep(i, 3) {
        if (A[i] + 1 != A[i + 1]) ans = "No\n";
    }
    cout << ans;
}