#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,c;
	cin>>a>>b>>c;
	if(a>b) swap(a,b);
	if(b>c) swap(b,c);
	if(a>b) swap(a,b);
	if(b-a==c-b) cout<<"Yes";
	else cout<<"No";
	return 0;
}