#include using namespace std; typedef long long ll; typedef pair p_ll; template void debug(T itr1, T itr2) { auto now = itr1; while(now=0; i--) const ll MOD = pow(10,9)+7; const ll LLINF = pow(2,61)-1; const int INF = pow(2,30)-1; vector fac; void c_fac(int x=pow(10,6)+10) { fac.resize(x,true); rep(i,x) fac[i] = i ? (fac[i-1]*i)%MOD : 1; } ll inv(ll a, ll m=MOD) { ll b = m, x = 1, y = 0; while (b!=0) { int d = a/b; a -= b*d; swap(a,b); x -= y*d; swap(x,y); } return (x+m)%m; } ll nck(ll n, ll k) { return fac[n]*inv(fac[k]*fac[n-k]%MOD)%MOD; } ll gcd(ll a, ll b) { if (a pos; SegTree(ll N) { size = 1; while(size>=1) operate(x); } ll query(ll a, ll b) { ll L = 0, R = 0; for (a+=size, b+=size; a>=1, b>>=1) { if (a&1) { L = q(L,pos[a]); a++; } if (b&1) { b--; R = q(R,pos[b]); } } return q(L,R); } void operate(ll i) { pos[i] = pos[i*2] + pos[i*2+1]; } ll q(ll x, ll y) { return x + y; } }; // ---------------------------------------------------------------------- // ---------------------------------------------------------------------- vector> adj; ll dfs(SegTree &st, ll n=0) { ll result = st.query(0,n); st.update(n,1); for (auto x: adj[n]) result += dfs(st, x); st.update(n,0); return result; } int main() { ll N; cin >> N; adj.resize(N); rep(i,N-1) { ll A; cin >> A; adj[A].push_back(i+1); } SegTree st(N); ll result = dfs(st); cout << result << endl; return 0; }