#include <iostream>
#include <algorithm>
using namespace std;
int main(){
	int a[4];
	for(int i=0;i<4;i++) cin >> a[i];
	sort(a,a+4);
	if(a[0]+1==a[1] && a[1]+1==a[2] && a[2]+1==a[3]){
		cout<<"Yes"<<endl;
	}else{
		cout<<"No"<<endl;
	}
	return 0;
}