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

int main() {
	cin.tie(nullptr);
	ios_base::sync_with_stdio(false);
	
	int P, Q, R;
	cin >> P >> Q >> R;
	cout << (Q*2 == P + R ? "Yes\n" : "No\n");
}