import java.io.*; import java.util.*; public class Main { public static void main(String[] args) throws Exception { Scanner sc = new Scanner(); int n = sc.nextInt(); int[] values = new int[n + 1]; for (int i = 1; i < n; i++) { values[i] = sc.nextInt(); } int[] costs = new int[n + 1]; Arrays.fill(costs, Integer.MAX_VALUE); costs[0] = 0; PriorityQueue queue = new PriorityQueue<>(); queue.add(new Path(1, 0)); while (queue.size() > 0) { Path p = queue.poll(); if (costs[p.idx] <= p.value) { continue; } costs[p.idx] = p.value; queue.add(new Path(values[p.idx], p.value + 1)); queue.add(new Path(p.idx - 1, p.value)); } System.out.println(costs[n]); } static class Path implements Comparable { int idx; int value; public Path(int idx, int value) { this.idx = idx; this.value = value; } public int compareTo(Path another) { return value - another.value; } } } class Scanner { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); StringTokenizer st = new StringTokenizer(""); public Scanner() throws Exception { } public int nextInt() throws Exception { return Integer.parseInt(next()); } public long nextLong() throws Exception { return Long.parseLong(next()); } public double nextDouble() throws Exception { return Double.parseDouble(next()); } public String next() throws Exception { while (!st.hasMoreTokens()) { st = new StringTokenizer(br.readLine()); } return st.nextToken(); } }