// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
int main() {
    // Input
    int A, B, C, D;
    cin >> A >> B >> C >> D;

    // Judge
    int a[4] = {A, B, C, D};
    sort(a, a + 4);

    bool ok = true;
    rep(i, 3) if (a[i + 1] != a[i] + 1) ok = false;

    // Output
    cout << (ok ? "Yes" : "No") << endl;
}