#pragma GCC optimize ("O3") #include "bits/stdc++.h" using namespace std; using ll = long long int; #define debugos cout #define debug(v) {printf("L%d %s > ",__LINE__,#v);debugos<<(v)< ",__LINE__,#v);for(auto e:(v)){debugos< ",__LINE__,#m);for(int x=0;x<(w);x++){debugos<<(m)[x]<<" ";}debugos<\n",__LINE__,#m);for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){debugos<<(m)[y][x]<<" ";}debugos< f) { if (!assertion) { cerr << "assertion fault:" << endl; f(); abort(); } } template inline ostream& operator <<(ostream &o, const pair p) { o << '(' << p.first << ':' << p.second << ')'; return o; } template inline ostream& _ostream_vecprint(ostream& os, const Vec& a) { os << '['; for (const auto& e : a) os << ' ' << e << ' '; os << ']'; return os; } template inline ostream& operator<<(ostream& o, const vector& v) { return _ostream_vecprint(o, v); } template inline ostream& operator<<(ostream& o, const array& v) { return _ostream_vecprint(o, v); } template inline T& chmax(T& to, const T& val) { return to = max(to, val); } template inline T& chmin(T& to, const T& val) { return to = min(to, val); } void bye(string s, int code = 0) { cout << s << endl; exit(code); } mt19937_64 randdev(8901016); template::value>::type* = nullptr> inline T rand(T l, T h, Random& rand = randdev) { return uniform_int_distribution(l, h)(rand); } template::value>::type* = nullptr> inline T rand(T l, T h, Random& rand = randdev) { return uniform_real_distribution(l, h)(rand); } #if defined(_WIN32) || defined(_WIN64) #define getchar_unlocked _getchar_nolock #define putchar_unlocked _putchar_nolock #elif defined(__GNUC__) #else #define getchar_unlocked getchar #define putchar_unlocked putchar #endif namespace { #define isvisiblechar(c) (0x21<=(c)&&(c)<=0x7E) class MaiScanner { public: template void input_integer(T& var) noexcept { var = 0; T sign = 1; int cc = getchar_unlocked(); for (; cc<'0' || '9'>(int& var) noexcept { input_integer(var); return *this; } inline MaiScanner& operator>>(long long& var) noexcept { input_integer(var); return *this; } inline MaiScanner& operator>>(string& var) { int cc = getchar_unlocked(); for (; !isvisiblechar(cc); cc = getchar_unlocked()); for (; isvisiblechar(cc); cc = getchar_unlocked()) var.push_back(cc); return *this; } template inline void in(IT begin, IT end) { for (auto it = begin; it != end; ++it) *this >> *it; } }; class MaiPrinter { public: template void output_integer(T var) noexcept { if (var == 0) { putchar_unlocked('0'); return; } if (var < 0) putchar_unlocked('-'), var = -var; char stack[32]; int stack_p = 0; while (var) stack[stack_p++] = '0' + (var % 10), var /= 10; while (stack_p) putchar_unlocked(stack[--stack_p]); } inline MaiPrinter& operator<<(char c) noexcept { putchar_unlocked(c); return *this; } inline MaiPrinter& operator<<(int var) noexcept { output_integer(var); return *this; } inline MaiPrinter& operator<<(long long var) noexcept { output_integer(var); return *this; } inline MaiPrinter& operator<<(char* str_p) noexcept { while (*str_p) putchar_unlocked(*(str_p++)); return *this; } inline MaiPrinter& operator<<(const string& str) { const char* p = str.c_str(); const char* l = p + str.size(); while (p < l) putchar_unlocked(*p++); return *this; } template void join(IT begin, IT end, char sep = ' ') { for (bool b = 0; begin != end; ++begin, b = 1) b ? *this << sep << *begin : *this <<* begin; } }; } MaiScanner scanner; MaiPrinter printer; template class Bitree { const int size_; vector data_; static int nlz(uint32_t x) { union { uint32_t i; float f; } data; data.f = (float)x + 0.5; return 158 - (data.i >> 23); } public: Bitree(int size_) :size_(size_), data_(size_+1) {} // 1..rの範囲の値の和を求める. T sum(int r) const { T s = 0; while (r) { s += data_[r]; r -= r&-r; // r&-r と書くことで最下のビットを得る } return s; } // l..rの範囲の値の和を求める inline T sum(int l, int r) const { return sum(r) - sum(l-1); } // i番目の値を求める(1index) T get(int i) const { int j = i - 1; T s = 0; while (i != j) { s += data_[i] - data_[j]; i -= i&-i; j -= j&-j; } return s; } // idxの要素の値をval増やす void add(int idx, T val) { while (idx <= size_) { data_[idx] += val; idx += idx&-idx; } } // sum(i)がvalを超える最初のiを返す // get(j)<0となるjが存在すると正しく動作しない int upper_bound(T val) const { int li = 1 << (31 - nlz(size_)); int p = 0; T d = 0; while (li && p < size_) { T k = data_[p | li]; if (!(val < d + k)) p |= li, d += k; li >>= 1; } if (p > size_) p = size_; return p+1; } // sum(i)がval以上である最初のiを返す // get(j)<0となるjが存在すると正しく動作しない int lower_bound(T val) const { int li = 1 << (31 - nlz(size_)); int p = 0; T d = 0; while (li && p < size_) { T k = data_[p | li]; if (d + k < val) p |= li, d += k; li >>= 1; } if (p > size_) p = size_; return p+1; } }; int N; int P[200010]; vector V[200010]; ll total = 0; void dfs(int idx, Bitree& parents){ total += parents.sum(idx); parents.add(idx+1, 1); for (int v : V[idx]) dfs(v, parents); parents.add(idx+1, -1); } int main(){ scanner >> N; scanner.in(P, P+N-1); repeat(i, N-1) V[P[i]].push_back(i+1); Bitree bit(N); dfs(0, bit); printer << total << '\n'; return 0; }