#include <stdio.h>
#define MAX 12345678

struct segTree{
	int value[400010];
	void setValue(int ind, int val, int l=1, int r=100000, int v=1)
	{
		if(l==r) value[v] = val;
		else
		{
			int h = (l+r)/2;
			if(ind<=h) setValue(ind,val,l,h,2*v);
			else setValue(ind,val,h+1,r,2*v+1);
			value[v] = value[2*v]<value[2*v+1]?value[2*v]:value[2*v+1];
		}
	}
	int getMin(int L, int R, int l=1, int r=100000, int v=1)
	{
		if(L<=l&&r<=R) return value[v];
		else if(r<L) return MAX;
		else if(R<l) return MAX;
		else
		{
			int h = (l+r)/2;
			int s1 = getMin(L,R,l,h,2*v);
			int s2 = getMin(L,R,h+1,r,2*v+1);
			return s1<s2?s1:s2;
		}
	}
}T;

int x[100010];
int main()
{
	int a;
	scanf("%d",&a);
	for(int i=1;i<a;i++) scanf("%d",&x[i]);
	for(int i=a-1;i>=1;i--) T.setValue(i,T.getMin(i+1,x[i])+1);
	printf("%d",T.getMin(1,1));
}