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

int main(){
    vector<int> n(4);
    for(int i=0;i<4;i++)cin >> n[i];
    sort(n.begin(),n.end());
    if(n[1]==n[0]+1&&n[2]==n[1]+1&&n[3]==n[2]+1) cout << "Yes" << endl;
    else cout << "No" << endl;
    
    return 0;
}