#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    vector<int> vc;
    for (int i = 0; i < 4; i++) {
        int in;
        cin >> in;
        vc.push_back(in);
    }
    sort(vc.begin(), vc.end());

    for (int i = 0; i < 3; i++) {
        if (vc.at(i) != vc.at(i + 1) - 1) {
            printf("No\n");
            return 1;
        }
    }
    printf("Yes\n");
    return 0;
}