#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    int n = 4;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    sort(a.begin(), a.end());

    int b = 1;
    for (int i = 1; i < n; i++) {
        if (a[i - 1] + 1 != a[i]) b = 0;
    }

    cout << (b ? "Yes" : "No") << endl;

    return 0;
}