#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("secv.in");
ofstream fout("secv.out");
#define Nmax 5005

int v[Nmax], el[Nmax], norm[Nmax], last[Nmax], best[Nmax];

int main()
{
    int i, j, n, MIN = Nmax + 5, nr;
    fin >> n;

    if(n == 0) {fout << -1 << '\n'; return 0;}
    if(n == 1) {fout << 1 << '\n'; return 0;}

    for(i = 1; i <= n; ++i) {fin >> v[i]; el[i] = v[i];}

    sort(el + 1, el + n + 1);
    for(i = j = 1; i <= n; ++j)
    {
        el[j] = el[i];
        while(el[j] == el[i]) ++i;
    }
    nr = j - 1;
    for(i = 1; i <= n; ++i) norm[i] = lower_bound(el + 1, el + nr + 1, v[i]) - el;

    for(i = 1; i <= n; ++i)
    {
        if(norm[i] == 1) best[i] = 1, last[1] = i;
        else if(last[norm[i] - 1])
        {
            best[i] = i - last[norm[i] - 1] + best[last[norm[i] - 1]];
            last[norm[i]] = i;
            if(norm[i] == nr && best[i] < MIN) MIN = best[i];
        }
    }

    if(MIN == Nmax + 5) fout << "-1\n";
    else fout << MIN << '\n';
    return 0;
}