#include using namespace std; //repetition #define FOR(i,a,b) for(ll i=(a);i<(b);++i) #define rep(i, n) for(ll i = 0; i < (ll)(n); i++) //container util #define all(x) (x).begin(),(x).end() //typedef typedef long long ll; typedef vector VI; typedef vector VVI; typedef vector VLL; typedef vector VVLL; typedef vector VS; typedef pair PII; typedef pair PLL; //const value //const ll MOD = 1e9 + 7; //const int dx[] = {0,1,0,-1};//{0,0,1,1,1,-1,-1,-1}; //const int dy[] = {1,0,-1,0};//{1,-1,0,1,-1,0,1,-1}; //conversion inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;} inline ll toLL(string s) {ll v; istringstream sin(s);sin>>v;return v;} template inline string toString(T x) {ostringstream sout;sout< 0 ; idx -= x & (-x)){ res += nodes[idx]; } return res; } }; ll dfs(int current_node, vector edge[], BIT & bit){ ll res = 0; // 二分探索をしてcurrent_nodeよりも小さい要素を探索 res += bit.sum(current_node); bit.add(current_node,1); for(int node :edge[current_node]){ res += dfs(node,edge,bit); } bit.add(current_node,-1); return res; } int main(){ ios::sync_with_stdio(false); cin.tie(0); int n; cin >> n; VI a(n); VI edge[n]; FOR(i,1,n){ cin >> a[i]; edge[a[i]].push_back(i); } BIT bit; bit.init(n); ll ans = dfs(0,edge,bit); cout << ans << endl; return 0; }