//@formatter:off
#include<bits/stdc++.h>
#define overload4(_1,_2,_3,_4,name,...) name
#define rep1(i,n) for (ll i = 0; i < ll(n); ++i)
#define rep2(i,s,n) for (ll i = ll(s); i < ll(n); ++i)
#define rep3(i,s,n,d) for(ll i = ll(s); i < ll(n); i+=d)
#define rep(...) overload4(__VA_ARGS__,rep3,rep2,rep1)(__VA_ARGS__)
#define rrep(i,n) for (ll i = ll(n)-1; i >= 0; i--)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define popcount(x) __builtin_popcount(x)
#define pb push_back
#define eb emplace_back
#ifdef __LOCAL
#define debug(...) { cout << #__VA_ARGS__; cout << ": "; print(__VA_ARGS__); cout << flush; }
#else
#define debug(...) void(0)
#endif
#define INT(...) int __VA_ARGS__;scan(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;scan(__VA_ARGS__)
#define STR(...) string __VA_ARGS__;scan(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__;scan(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__;scan(__VA_ARGS__)
#define LD(...) ld __VA_ARGS__;scan(__VA_ARGS__)
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<int,int>;
using LP = pair<ll,ll>;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vd = vector<double>;
using vvd = vector<vector<double>>;
using vs = vector<string>;
using vc = vector<char>;
using vvc = vector<vector<char>>;
using vb = vector<bool>;
using vvb = vector<vector<bool>>;
using vp = vector<P>;
using vvp = vector<vector<P>>;
template<class S,class T> istream& operator>>(istream &is,pair<S,T> &p) { return is >> p.first >> p.second; }
template<class S,class T> ostream& operator<<(ostream &os,const pair<S,T> &p) { return os<<'{'<<p.first<<","<<p.second<<'}'; }
template<class T> istream& operator>>(istream &is,vector<T> &v) { for(T &t:v){is>>t;} return is; }
template<class T> ostream& operator<<(ostream &os,const vector<T> &v) { os<<'[';rep(i,v.size())os<<v[i]<<(i==int(v.size()-1)?"":","); return os<<']'; }
template<class T> void vecout(const vector<T> &v,char div='\n') { rep(i,v.size()) cout<<v[i]<<(i==int(v.size()-1)?'\n':div);}
template<class T> bool chmin(T& a,T b) {if(a > b){a = b; return true;} return false;}
template<class T> bool chmax(T& a,T b) {if(a < b){a = b; return true;} return false;}
void scan(){}
template <class Head, class... Tail> void scan(Head& head, Tail&... tail){ cin >> head; scan(tail...); }
template<class T> void print(const T& t){ cout << t << '\n'; }
template <class Head, class... Tail> void print(const Head& head, const Tail&... tail){ cout<<head<<' '; print(tail...); }
template<class... T> void fin(const T&... a) { print(a...); exit(0); }
const string yes[] = {"no","yes"};
const string Yes[] = {"No","Yes"};
const string YES[] = {"NO","YES"};
const int inf = 1001001001;
const ll linf = 1001001001001001001;
//@formatter:on

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    INT(n);
    vvi G(n);
    rep(i, 1, n) {
        INT(p);
        p--;
        G[p].pb(i);
    }
    auto dfs = [&](auto &self, int u) -> P {
        vi ev, od;
        int st = 1;
        for (int v : G[u]) {
            auto[sc, t] = self(self, v);
            if (t) od.pb(-sc);
            else ev.pb(-sc);
            st += t;
        }
        sort(all(ev));
        sort(all(od));
        int res = 1;
        while (ev.size() and ev.back() >= 0) {
            res -= ev.back();
            ev.pop_back();
        }
        int t = -1;
        while (od.size()) {
            res += od.back() * t;
            od.pop_back();
            t *= -1;
        }
        for (int i : ev) res += i * t;
        return {res, st & 1};
    };
    auto[ans, _] = dfs(dfs, 0);
    ans += n;
    assert(ans % 2 == 0);
    ans /= 2;
    print(ans);
}

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define endl "\n"
#define speed ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define pb push_back
#define F first
#define S second
#define um map <ll,ll>
#define rep(i,z,n)  for(int i=z;i<n;i++)
#define repi(i,z,n) for(int i=z;i<=n;i++)
#define repn(i,z,n) for(int i=n-1;i>=z;i--)
#define vec vector<ll>
#define vecp vector<pair<ll,ll>>
// #define pi (double)3.14159265358979323846
#define ld long double
#define all(z) z.begin(),z.end()
#define pii pair<ll,ll>

ll power(ll a, ll b, ll m) { ll ans = 1; a = a % m; if (a == 0) return 0; while (b) { if (b & 1) ans = (ans * a) % m; b /= 2; a = (a * a) % m; } return ans; }
ll modInverse(ll a, ll m) {return power(a, m - 2, m);}
ll binpow(ll a, ll b) {ll res = 1; while (b > 0) {if (b & 1)res = res * a; a = a * a; b >>= 1;} return res;}
ll binlog2(ll n) {ll logValue = -1; while (n) {logValue++; n >>= 1;} return logValue;}
ll ceil(ll t1, ll t2) {ll ans = (t1 + t2 - 1) / t2; return ans;}
void print(vec a) {rep(i, 0, a.size())cout << a[i] << " "; cout << endl;}
const ll mod = 1e9 + 7;
const ll N = 30 + 5;
const ll inf = 2e18;



void solve() {
    vec a(3);
    rep(i, 0, 3)
    cin >> a[i];

    sort(all(a));

    if (a[1] - a[0] == a[2] - a[1])
        cout << "Yes" << endl;
    else
        cout << "No" << endl;

}

int main() {
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    speed;
    int test = 1;
    // init();
    // cin >> test;
    // ll t1 = 1;
    while (test--) {
        // cout << "Case #" << t1 << ": ";
        solve();
        // t1++;
    }
    return 0;
}