#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 (c-b==b-a) cout<<"Yes";else cout<<"No";
	return 0;
}