#include<bits/stdc++.h>

using namespace std;

int a[4];

int main(){
    cin >> a[0] >> a[1] >> a[2] >> a[3];
    sort(a, a + 4);
    cout << (a[0]+1==a[1]&&a[1]+1==a[2]&&a[2]+1==a[3] ? "Yes" : "No") << endl;
}