package adv2018; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.InputMismatchException; public class Day26 { InputStream is; PrintWriter out; String INPUT = ""; void solve() { int n = ni(); int[] par = new int[n]; par[0] = -1; for(int i = 1;i < n;i++){ par[i] = ni(); } int[][] ch = parentToChildren(par); ans = 0; dfs(0, new int[n+3], ch); out.println(ans); } void dfs(int cur, int[] ft, int[][] ch) { ans += sumFenwick(ft, cur); addFenwick(ft, cur, 1); for(int e : ch[cur]){ dfs(e, ft, ch); } addFenwick(ft, cur, -1); } long ans = 0; public static int[][] parentToChildren(int[] par) { int n = par.length; int[] ct = new int[n]; for(int i = 0;i < n;i++){ if(par[i] >= 0){ ct[par[i]]++; } } int[][] g = new int[n][]; for(int i = 0;i < n;i++){ g[i] = new int[ct[i]]; } for(int i = 0;i < n;i++){ if(par[i] >= 0){ g[par[i]][--ct[par[i]]] = i; } } return g; } public static int sumFenwick(int[] ft, int i) { int sum = 0; for(i++;i > 0;i -= i&-i)sum += ft[i]; return sum; } public static void addFenwick(int[] ft, int i, int v) { if(v == 0 || i < 0)return; int n = ft.length; for(i++;i < n;i += i&-i)ft[i] += v; } public static int[][] parentToG(int[] par) { int n = par.length; int[] ct = new int[n]; for(int i = 0;i < n;i++){ if(par[i] >= 0){ ct[i]++; ct[par[i]]++; } } int[][] g = new int[n][]; for(int i = 0;i < n;i++){ g[i] = new int[ct[i]]; } for(int i = 0;i < n;i++){ if(par[i] >= 0){ g[par[i]][--ct[par[i]]] = i; g[i][--ct[i]] = par[i]; } } return g; } void run() throws Exception { is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); // // long s = System.currentTimeMillis(); // solve(); // out.flush(); // if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){ @Override public void run() { long s = System.currentTimeMillis(); solve(); out.flush(); if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); } }; t.start(); t.join(); } public static void main(String[] args) throws Exception { new Day26().run(); } private byte[] inbuf = new byte[1024]; public int lenbuf = 0, ptrbuf = 0; private int readByte() { if(lenbuf == -1)throw new InputMismatchException(); if(ptrbuf >= lenbuf){ ptrbuf = 0; try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); } if(lenbuf <= 0)return -1; } return inbuf[ptrbuf++]; } private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; } private double nd() { return Double.parseDouble(ns()); } private char nc() { return (char)skip(); } private String ns() { int b = skip(); StringBuilder sb = new StringBuilder(); while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ') sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } private char[] ns(int n) { char[] buf = new char[n]; int b = skip(), p = 0; while(p < n && !(isSpaceChar(b))){ buf[p++] = (char)b; b = readByte(); } return n == p ? buf : Arrays.copyOf(buf, p); } private int[] na(int n) { int[] a = new int[n]; for(int i = 0;i < n;i++)a[i] = ni(); return a; } private long[] nal(int n) { long[] a = new long[n]; for(int i = 0;i < n;i++)a[i] = nl(); return a; } private char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } private int[][] nmi(int n, int m) { int[][] map = new int[n][]; for(int i = 0;i < n;i++)map[i] = na(m); return map; } private int ni() { return (int)nl(); } private long nl() { long num = 0; int b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); } }