#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int p, q, r;
  cin >> p >> q >> r;
  cout << (2 * q == p + r ? "Yes" : "No") << '\n';
  return 0;
}