#include <bits/stdc++.h>

#include <atcoder/all>
#define rep(i, a, b) for (ll i = (ll)(a); i < (ll)(b); i++)
using namespace atcoder;
using namespace std;

typedef long long ll;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(12);
    ll a, b, c;
    cin >> a >> b >> c;
    string ans;
    if (b + b == a + c)
        ans = "Yes";
    else
        ans = "No";
    cout << ans << endl;
}