#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 10000000000000000

int main(){
	
	vector<int> A(4);
	
	for(int i=0;i<4;i++)cin>>A[i];
	
	sort(A.begin(),A.end());
	
	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;
}