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

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