#include <bits/stdc++.h>

using namespace std;

int main() {
    int a, b, c, d;

    cin >> a >> b >> c >> d;
    
    int vec[4] = { a, b, c, d };
    sort(vec, vec+4);

    if (vec[1] == vec[0] + 1 && vec[2] == vec[1] + 1 && vec[3] == vec[2] + 1) {
        puts("Yes");
    } else {
        puts("No");
    }

    return 0;
}