Vasya commutes by train every day. There are n train stations in the city, and at the i-th station it's possible to buy only tickets to stations from i + 1 to ai inclusive. No tickets are sold at the last station.

Let ρi, j be the minimum number of tickets one needs to buy in order to get from stations i to station j. As Vasya is fond of different useless statistic he asks you to compute the sum of all values ρi, j among all pairs 1 ≤ i < j ≤ n.

Input

The first line of the input contains a single integer n (2 ≤ n ≤ 100 000) — the number of stations.

The second line contains n - 1 integer ai (i + 1 ≤ ai ≤ n), the i-th of them means that at the i-th station one may buy tickets to each station from i + 1 to ai inclusive.

Output

Print the sum of ρi, j among all pairs of 1 ≤ i < j ≤ n.

Examples

Input

4
4 4 4


Output

6


Input

5
2 3 5 5


Output

17

Note

In the first sample it's possible to get from any station to any other (with greater index) using only one ticket. The total number of pairs is 6, so the answer is also 6.

Consider the second sample: 

  * ρ1, 2 = 1
  * ρ1, 3 = 2
  * ρ1, 4 = 3
  * ρ1, 5 = 3
  * ρ2, 3 = 1
  * ρ2, 4 = 2
  * ρ2, 5 = 2
  * ρ3, 4 = 1
  * ρ3, 5 = 1
  * ρ4, 5 = 1



Thus the answer equals 1 + 2 + 3 + 3 + 1 + 2 + 2 + 1 + 1 + 1 = 17.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.nio.channels.SeekableByteChannel;
import java.util.*;
import java.util.stream.Stream;

public class TestClass implements Runnable {
	
	static final double time = 1e9;
	static final int MOD = (int) 1e9 + 7;
	static final long mh = Long.MAX_VALUE;
	static final Reader in = new Reader();
	static final PrintWriter out = new PrintWriter(System.out);
	StringBuilder answer = new StringBuilder();

	public static void main(String[] args) {
		new Thread(null, new TestClass(), "persefone", 1 << 28).start();
	}

	@Override
	public void run() {
		long start = System.nanoTime();
		solve();		
		printf();
		long elapsed = System.nanoTime() - start;
//		out.println("stamp : " + elapsed / time);
//		out.println("stamp : " + TimeUnit.SECONDS.convert(elapsed, TimeUnit.NANOSECONDS));
		close();
	}
	
	void solve() {
		int n = in.nextInt();
		int[] a = new int[n];
		for (int i = 1; i < n; i++) a[i] = in.nextInt();

		long[] dp = new long[n];
		long ans = 0;
		SegmentTreeMax segmentTreeMax = new SegmentTreeMax(a, n);
		for (int i = n - 1; i > 0; i--) {
			if (a[i] == n)  ans += dp[i] = n - i;
			else {
				int posMax = segmentTreeMax.getMax(i + 1, a[i])[1];
				ans += dp[i] = dp[posMax] + posMax - i + (n - a[i]);
			}
		}
		printf(ans);
	}

	static class SegmentTreeMax {
		private int n;
		private int[] a;
		private int[][] max;

		public SegmentTreeMax(int[] a, int n) {
			this.a = a;
			this.n = n;
			max = new int[4 * n + 4][2];
			build(1, 0, n - 1);
		}

		private int[] merge(int[] x, int[] y) {
			if (x[0] > y[0]) return x;
			if (y[0] > x[0]) return y;
			if (x[1] > y[1]) return x;
			return y;
		}

		private void build(int currentVertex, int currentLeft, int currentRight) {
			if (currentLeft == currentRight) max[currentVertex] = new int[] { a[currentLeft], currentLeft };
			else {
				int middle = currentLeft + currentRight >>> 1, doubleVex = currentVertex << 1;
				build(doubleVex, currentLeft, middle);
				build(doubleVex + 1, middle + 1, currentRight);
				max[currentVertex] = merge(max[doubleVex], max[doubleVex + 1]);
			}
		}

		private void update(int currentVertex, int currentLeft, int currentRight, int pos, int value) {
			if (currentLeft == currentRight) max[currentVertex] = new int[] { a[pos] = value, pos };
			else {
				int middle = currentLeft + currentRight >>> 1, doubleVex = currentVertex << 1;
				if (pos <= middle)
					update(doubleVex, currentLeft, middle, pos, value);
				else
					update(doubleVex + 1, middle + 1, currentRight, pos, value);
				max[currentVertex] = merge(max[doubleVex], max[doubleVex + 1]);
			}
		}

		public void update(int pos, int value) {
			if (pos < 0 || pos >= n) throw new RuntimeException();
			update(1, 0, n - 1, pos, value);
		}

		private int[] getMax(int currentVertex, int currentLeft, int currentRight, int left, int right) {
			if (left > currentRight || right < currentLeft) return new int[] {-1, -1};
			if (currentLeft >= left && currentRight <= right) return max[currentVertex];
			int middle = currentLeft + currentRight >>> 1, doubleVex = currentVertex << 1;
			return merge(getMax(doubleVex, currentLeft, middle, left, right),
					getMax(doubleVex + 1, middle + 1, currentRight, left, right));
		}

		public int[] getMax(int left, int right) {
			return getMax(1, 0, n - 1, left, right);
		}

	}

	static class ArrayUtils {

		static void compressed(long[] a, int n) {
			long[] b = a.clone();
			Arrays.sort(b);
			for (int i = 0; i < n; i++) a[i] = lw(b, 0, n, a[i]) + 1;
		}

		static int lw(long[] b, int l, int r, long k) {
			int m = 0, ans = r;
			while (l < r) if (Long.compare(b[m = l + r >> 1], k) >= 0) ans = r = m; else l = m + 1;
			return ans;
		}

		static <T> int upperBound(T[] arr, int start, int end, T t, Comparator<? super T> c) {
			int ans = end;
			while (start < end) {
				int mid = start + end >>> 1;
				if (c.compare(arr[mid], t) > 0) ans = end = mid; else start = mid + 1;
			}
			return ans;
		}

		static <T> int lowerBound(T[] arr, int start, int end, T t, Comparator<? super T> c) {
			int ans = end;
			while (start < end) {
				int mid = start + end >>> 1;
				if (c.compare(arr[mid], t) >= 0) ans = end = mid; else start = mid + 1;
			}
			return ans;
		}
	}

	int pow(int a, int b, int p) {
		long ans = 1, base = a;
		while (b > 0){
			if ((b & 1) > 0) {
				ans *= base %= p;
			}
			base *= base %= p;
			b >>= 1;
		}
		return (int)ans;
	}
	
	public static int[] enumLowestPrimeFactors(int n) {
		int tot = 0;
		int[] lpf = new int[n + 1];
		int u = n + 32;
		double lu = Math.log(u);
		int[] primes = new int[(int) (u / lu + u / lu / lu * 1.5)];
		for (int i = 2; i <= n; i++)
			lpf[i] = i;
		for (int p = 2; p <= n; p++) {
			if (lpf[p] == p)
				primes[tot++] = p;
			int tmp;
			for (int i = 0; i < tot && primes[i] <= lpf[p] && (tmp = primes[i] * p) <= n; i++) {
				lpf[tmp] = primes[i];
			}
		}
		return lpf;
	}

	
	public static int[] enumNumDivisorsFast(int n, int[] lpf)
	{
		int[] nd = new int[n+1];
		nd[1] = 1;
		for(int i = 2;i <= n;i++){
			int j = i, e = 0;
			while(j % lpf[i] == 0){
				j /= lpf[i];
				e++;
			}
			nd[i] = nd[j] * (e+1);
		}
		return nd;
	}
	
	boolean isPrime(long n) {
		
		for (int i = 2; 1l * i * i <= n; i++) 
			if (n % i == 0)
				return false;
		return true;
	}
	
	void printf() {
		out.print(answer);
	}
	
	void close() {
		out.close();
	}

	void printf(Stream<?> str) {
		str.forEach(o -> add(o, " "));
		add("\n");
	}

	 
	void printf(Object... obj) {
		printf(false, obj);
	}

	void printfWithDescription(Object... obj) {
		printf(true, obj);
	}
	
		
	private void printf(boolean b, Object... obj) {

		if (obj.length > 1) {
			for (int i = 0; i < obj.length; i++) {
				if (b) add(obj[i].getClass().getSimpleName(), " - ");
				if (obj[i] instanceof Collection<?>) {
					printf((Collection<?>) obj[i]);
				} else if (obj[i] instanceof int[][]) {
					printf((int[][])obj[i]);
				} else if (obj[i] instanceof long[][]) {
					printf((long[][])obj[i]);
				} else if (obj[i] instanceof double[][]) {
					printf((double[][])obj[i]);
				} else printf(obj[i]);
			}
			return;
		}

		if (b) add(obj[0].getClass().getSimpleName(), " - ");
		printf(obj[0]);
	}

	void printf(Object o) {
		if (o instanceof int[])
			printf(Arrays.stream((int[]) o).boxed());
		else if (o instanceof char[])
			printf(new String((char[]) o));
		else if (o instanceof long[])
			printf(Arrays.stream((long[]) o).boxed());
		else if (o instanceof double[])
			printf(Arrays.stream((double[]) o).boxed());
		else if (o instanceof boolean[]) {
			for (boolean b : (boolean[]) o) add(b, " ");
			add("\n");
		}
		else 
			add(o, "\n");
	}

	void printf(int[]... obj) {
		for (int i = 0; i < obj.length; i++) printf(obj[i]);
	}
	
	void printf(long[]... obj) {
		for (int i = 0; i < obj.length; i++) printf(obj[i]);
	}
	
	void printf(double[]... obj) {
		for (int i = 0; i < obj.length; i++) printf(obj[i]);
	}
	
	void printf(boolean[]... obj) {
		for (int i = 0; i < obj.length; i++) printf(obj[i]);
	}
	
	void printf(Collection<?> col) {
		printf(col.stream());
	}

	<T, K> void add(T t, K k) {
		if (t instanceof Collection<?>) {
			((Collection<?>) t).forEach(i -> add(i, " "));
		} else if (t instanceof Object[]) {
			Arrays.stream((Object[]) t).forEach(i -> add(i, " "));
		} else
			add(t);
		add(k);
	}
	
	
	
	<T> void add(T t) {
		answer.append(t);
	}

	@SuppressWarnings("unchecked")
	<T extends Comparable<? super T>> T min(T... t) {
		if (t.length == 0)
			return null;
		T m = t[0];
		for (int i = 1; i < t.length; i++)
			if (t[i].compareTo(m) < 0)
				m = t[i];
		return m;
	}

	@SuppressWarnings("unchecked")
	<T extends Comparable<? super T>> T max(T... t) {
		if (t.length == 0)
			return null;
		T m = t[0];
		for (int i = 1; i < t.length; i++)
			if (t[i].compareTo(m) > 0)
				m = t[i];
		return m;
	}

	int gcd(int a, int b) {
		return (b == 0) ? a : gcd(b, a % b);
	}

	long gcd(long a, long b) {
		return (b == 0) ? a : gcd(b, a % b);
	}
	
	long lcm(int a, int b) {
		return (1l * a * b / gcd(a, b));
	}
	
	long lcm(long a, long b) {
		if (a > Long.MAX_VALUE / b) throw new RuntimeException();
		return a * b / gcd(a, b);
	}
	
	// c = gcd(a, b) -> extends gcd method: ax + by = c <----> (b % a)p + q = c;
	int[] ext_gcd(int a, int b) {
		if (b == 0) return new int[] {a, 1, 0 };
		int[] vals = ext_gcd(b, a % b);
		int d = vals[0]; // gcd
	    int p = vals[2]; // 
		int q = vals[1] - (a / b) * vals[2];
		return new int[] { d, p, q };	  
	}
	
	// find any solution of the equation: ax + by = c using extends gcd
	boolean find_any_solution(int a, int b, int c, int[] root) {
		int[] vals = ext_gcd(Math.abs(a), Math.abs(b));
		if (c % vals[0] != 0) return false;
		printf(vals);
		root[0] = c * vals[1] / vals[0];
		root[1] = c * vals[2] / vals[0];
		if (a < 0) root[0] *= -1;
		if (b < 0) root[1] *= -1;
		return true;
	}
	
	int mod(int x) { return x % MOD; }
	
	int mod(int x, int y) { return mod(mod(x) + mod(y)); }
	
	long mod(long x) { return x % MOD; }
	
	long mod (long x, long y) { return mod(mod(x) + mod(y)); }
	
	int lw(long[] f, int l, int r, long k) {
		int R = r, m = 0;
		while (l <= r) {
			m = l + r >> 1;
		    if (m == R) return m;
		    if (f[m] >= k) r = m - 1; else l = m + 1;
		}
		return l;
	}
	
	int up(long[] f, int l, int r, long k) {
		int R = r, m = 0;
		while (l <= r) {
			m = l + r >> 1;
		    if (m == R) return m;
		    if (f[m] > k) r = m - 1; else l = m + 1;
		}
		return l;
	}
	
	int lw(int[] f, int l, int r, int k) {
		int R = r, m = 0;
		while (l <= r) {
			m = l + r >> 1;
		    if (m == R) return m;
		    if (f[m] >= k) r = m - 1; else l = m + 1;
		}
		return l;
	}
	
	int up(int[] f, int l, int r, int k) {
		int R = r, m = 0;
		while (l <= r) {
			m = l + r >> 1;
		    if (m == R) return m;
		    if (f[m] > k) r = m - 1; else l = m + 1;
		}
		return l;
	}
	
	int lw(double[] f, int l, int r, double k) {
		int R = r, m = 0;
		while (l <= r) {
			m = l + r >> 1;
		    if (m == R) return m;
		    if (f[m] >= k) r = m - 1; else l = m + 1;
		}
		return l;
	}
	
	int up(double[] f, int l, int r, double k) {
		int R = r, m = 0;
		while (l <= r) {
			m = l + r >> 1;
		    if (m == R) return m;
		    if (f[m] > k) r = m - 1; else l = m + 1;
		}
		return l;
	}

	<K extends Comparable<K>> int lw(List<K> li, int l, int r, K k) {
		int R = r, m = 0;
		while (l <= r) {
			m = l + r >> 1;
		    if (m == R) return m;
		    if (li.get(m).compareTo(k) >= 0) 
		    	r = m - 1;
		    else 
		    	l = m + 1;
		}
		return l;
	}
	
	<K extends Comparable<K>> int up(List<K> li, int l, int r, K k) {
		int R = r, m = 0;
		while (l <= r) {
			m = l + r >> 1;
		    if (m == R) return m;
		    if (li.get(m).compareTo(k) > 0) 
		    	r = m - 1;
		    else 
		    	l = m + 1;
		}
		return l;
	}
		
	<K extends Comparable<K>> int bs(List<K> li, int l, int r, K k) {
		while (l <= r) {
			int m = l + r >> 1;
		    if (li.get(m) == k) return m;
		    else if (li.get(m).compareTo(k) < 0)
		    	l = m + 1;
		    else 
		    	r = m - 1;
		}
		return -1;
	}
	
	long calc(int base, int exponent, int p) {
		if (exponent == 0) return 1;
		if (exponent == 1) return base % p;
		long m = calc(base, exponent >> 1, p);
		if (exponent % 2 == 0) return (m * m) % p;
		return 1l * base * m  % p * m % p;
	}
	
	long calc(int base, long exponent, int p) {
		if (exponent == 0) return 1;
		if (exponent == 1) return base % p;
		long m = calc(base, exponent >> 1, p);
		if (exponent % 2 == 0) return (m * m) % p;
		return 1l * base * m  % p * m % p;
	}
	
	long calc(long base, long exponent, int p) {
		if (exponent == 0) return 1;
		if (exponent == 1) return base % p;
		long m = calc(base, exponent >> 1, p);
		if (exponent % 2 == 0) return (m * m) % p;
		return base * m  % p * m % p;
	}
	
	long power(int base, int exponent) {
		if (exponent == 0) return 1;
		long m = power(base, exponent / 2);
		if (exponent % 2 == 0) return m * m;
		return base * m * m;
	}
	
	void swap(int[] a, int i, int j) {
		a[i] ^= a[j];
		a[j] ^= a[i];
		a[i] ^= a[j];
	}
	
	void swap(long[] a, int i, int j) {
		long tmp = a[i];
		a[i] = a[j];
		a[j] = tmp;
	}
	
	static class Pair<K extends Comparable<? super K>, V extends Comparable<? super V>>
			implements Comparable<Pair<K, V>> {
		private K k;
		private V v;

		Pair() {}

		Pair(K k, V v) {
			this.k = k;
			this.v = v;
		}

		K getK() { return k; }

		V getV() { return v; }

		void setK(K k) { this.k = k; }

		void setV(V v) { this.v = v; }

		void setKV(K k, V v) {
			this.k = k;
			this.v = v;
		}

		@SuppressWarnings("unchecked")
		@Override
		public boolean equals(Object o) {
			if (this == o) return true;
			if (o == null || !(o instanceof Pair)) return false;
			Pair<K, V> p = (Pair<K, V>) o;
			return k.compareTo(p.k) == 0 && v.compareTo(p.v) == 0;
		}

		@Override
		public int hashCode() {
			int hash = 31;
			hash = hash * 89 + k.hashCode();
			hash = hash * 89 + v.hashCode();
			return hash;
		}

		@Override
		public int compareTo(Pair<K, V> pair) {
			return k.compareTo(pair.k) == 0 ? v.compareTo(pair.v) : k.compareTo(pair.k);
		}

		@Override
		public Pair<K, V> clone() {
			return new Pair<K, V>(this.k, this.v);
		}

		@Override
		public String toString() {
			return String.valueOf(k).concat(" ").concat(String.valueOf(v)).concat("\n");
		}
	}

	static class Reader {
		private BufferedReader br;
		private StringTokenizer st;

		Reader() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			try {
				while (st == null || !st.hasMoreTokens()) {
					st = new StringTokenizer(br.readLine());
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		int[] nextIntArray(int n) {
			int[] arr = new int[n];
			for (int i = 0; i < n; i++)
				arr[i] = nextInt();
			return arr;
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		String nextLine() {
			String s = "";
			try {
				s = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return s;
		}
	}
}