#include<bits/stdc++.h>
using namespace std;
int main()
{
  int P , Q , R; cin >> P >> Q >> R;
  assert( -10 <= P && P <= 10 );
  assert( -10 <= Q && Q <= 10 );
  assert( -10 <= R && R <= 10 );
  assert( P != Q );
  assert( Q != R );
  assert( R != P );
  cout << ( Q * 2 == P + R ? "Yes" : "No" ) << "\n";
}