#include<iostream>
#include<algorithm>
using namespace std;
int main(){
	int a[4];
	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;
}