#include <iostream>
#include <cmath>
#include <cstdlib>
#include <cstdio>
#include <string>
#include <cstring>
#include <set>
#include <algorithm>
using namespace std;
int a[1001],b,c,d,k[6][2],f[1001],t;
int main(void)
{
	freopen ("seqgame.in","r",stdin);
	freopen ("seqgame.out","w",stdout);
	scanf("%d",&b);
	for (c=1;c<=b;c++) 
	{
		scanf("%d",&a[c]);
		if (a[c]>c) a[c]=0;
	}
	for (c=1;c<=b;c++)
		if (a[c]!=0)
		{
			if (c==1) f[c]=1;
				else 
				{
					for (d=c-1;d>=1;d--)
						if ((a[c]>a[d])&&(a[d]!=0)) f[c]=f[c]>f[d]+1?f[c]:f[d]+1;
				}
		}
	for (c=1;c<=b;c++)
		if (t<f[c]) t=f[c];
	printf("%d",t);
	fclose(stdin);
	fclose(stdout);
	return 0;
}