#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
// Welcome to my source code!

int main() {
    int n[4];
    cin >> n[0] >> n[1] >> n[2] >> n[3];
    sort(n, n+4);
    int top = n[0];
    bool flag = true;
    for (int i = 1; i < 4; i++) {
        if (top + 1 != n[i]) flag = false;
        top = n[i];
    }
    if (flag) cout << "Yes" << endl;
    else cout << "No" << endl;
}