#include <fstream>
#include <algorithm>
#include <set>
#include <limits.h>
using namespace std;

ifstream fin("secv.in");
ofstream fout("secv.out");

const int NMAX = 5003;
int n, a, b[NMAX], c[NMAX], maxi, ind_st;

set<int> nr;

int main()
{
	fin >> n;
	fill(b + 1, b + n + 1, INT_MAX);

	for (int i = 1; i <= n; ++i)
	{
		fin >> a;
		nr.insert(a);
		c[i] = lower_bound(b, b + n + 1, a) - b;
		if (c[i] > maxi)
			maxi = c[i];
		b[c[i]] = a;
	}

	fout << "-1\n";

	/*if (maxi != nr.size())
	{
		fout << "-1\n";
		return 0;
	}

	int s_min = n + 1;

	for (int i = n; i >= 1; --i)
	{
		if (c[i] == maxi)
		{
			int crt = maxi;
			for (int j = i; j; --j)
			{
				if (c[j] == crt)
				{
					--crt;
					if (crt == 0)
					{
						if (i - j + 1 < s_min)
							s_min = i - j + 1;
						break;
					}
				}
			}
		}
	}

	fout << s_min << "\n";
	*/
	return 0;
}