#include <bits/stdc++.h>
using namespace std;

int main() {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    int v[4] = { a, b, c, d };
    sort(v, v + 4);
    for (int i = 1; i < 4; i++) {
        if (v[i] != v[i - 1] + 1) {
            puts("No");
            return 0;
        }
    }
    puts("Yes");
}