#include<stdio.h>
int min(int a, int b)
{
	if (a < b)
		return a;
	else
		return b;
}
int r[100005];
int seg[400005], ss;
void update(int x, int v)
{
	x += ss - 1;
	seg[x] = v;
	while (x > 0)
	{
		x = (x - 1) / 2;
		seg[x] = min(seg[2 * x + 1], seg[2 * x + 2]);
	}
	return;
}
int getmin(int l, int r)
{
	l += ss - 1;
	r += ss - 1;
	int res = 1e9;
	while (l < r)
	{
		res = min(res, min(seg[l], seg[r]));
		l /= 2;
		r = r / 2 - 1;
	}
	if (l == r)
		res = min(res, seg[l]);
	return res;
}
int main()
{
	int n;
	scanf("%d", &n);
	int i;
	for (i = 0; i < n - 1; i++)
		scanf("%d", &r[i]);
	for (ss = 1; ss < n; ss *= 2);
	for (i = 0; i < 2 * ss - 1; i++)
		seg[i] = 1e9;
	update(n - 1, 0);
	for (i = n - 2; i >= 0; i--)
		update(i, 1 + getmin(i + 1, r[i] - 1));
	printf("%d\n", seg[ss - 1]);
	return 0;
}