#include <iostream>
#include <algorithm>

using namespace std;

int main() {
    int nums[4];
    for (int i = 0; i < 4; i++)
        cin >> nums[i];

    sort(nums, nums+4);

    bool ok = true;
    for (int i = 0; i < 3; i++) {
        if (nums[i + 1] - nums[i] != 1) {
            ok = false;
            break;
        }
    }

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

    return 0;
}