#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);
    for(int i = 0; i < 3; i++)
    {
        if(nums[i + 1] - nums[i] == 1)
        {
            continue;
        }
        else
        {
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
    return 0;
}