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

int main(int argc, const char *argv[])
{
    std::ios::sync_with_stdio(false);
    int nums[4];
    for (int i = 0; i < 4; i++) {
        cin >> nums[i];
    }
    sort(nums, nums+4);
    for (int i = 1; i < 4; i++) {
        if (nums[i] != nums[i-1] + 1) {
            std::cout << "No" << std::endl;
            return 0;
        }
    }
    std::cout << "Yes" << std::endl;
    return 0;
}