#include <fstream>

using namespace std;

ifstream f("secv.in");
ofstream g("secv.out");

int ord[5001], v[5001];
int n, i, j, max1, st, dr, min1;

int main()
{
    f >> n;
    for (i = 1; i <= n; i++)
        f >> v[i];
    ord[n] = 1;
    for (i = n-1; i >= 1; i--)
    {
        max1 = 0;
        for (j = i+1; j <= n; j++)
            if (max1 < ord[j] && v[i] < v[j])
                max1 = ord[j];
        ord[i] = max1+1;
    }
    max1 = 1, st = dr = 1, min1 = 1999999999;
    for (i = 1; i <= n; i++)
    {
        if (ord[i] > max1)
            max1 = ord[i], st = i;
        if (ord[i] < min1)
            min1 = ord[i], dr = i;
    }
    if (max1 > 1)
        g << dr-st+1;
    else
        g << -1;

    return 0;
}