/*http://www.infoarena.ro/problema/secv*/
#include <cstdio>
#include <unordered_set>
#define N 5001
using namespace std;
unordered_set<int> myset;
int v[N], st[N], sol[N], n, i, nr_dist;

int dinamica()
{
    int scmax = 1, minn = n;

    for(int i=1; i<n; ++i)
    {
        for(int j=i-1; j>=0; --j)
            if(v[j] < v[i] && (sol[i] < sol[j]+1 || (sol[i] == sol[j]+1 && st[j]>st[i])))
            {
                sol[i] = sol[j]+1;
                st[i] = st[j];
            }
        if(sol[i] > scmax)
            scmax = sol[i];
    }
    ++scmax;
    if(scmax < nr_dist) return -1;
    --nr_dist;
    for(int i=0; i<n; ++i)
        if(sol[i] == nr_dist && i - st[i] < minn)
            minn = i - st[i];
    return minn + 1;
}

int main()
{
    freopen("secv.in", "r", stdin);
    freopen("secv.out", "w", stdout);
    scanf("%d", &n);
    for(i=0; i<n; ++i)
    {
        scanf("%d", v+i);
        myset.insert(v[i]);
        st[i] = i;
    }
    nr_dist = myset.size();
    printf("%d\n", dinamica());
    return 0;
}