#include <bits/stdc++.h>
using namespace std;
ifstream in("secv.in");
ofstream out("secv.out");
const int N = 5005;
int v[N],dp[N],lst[N],viz[N];
int main()
{
    int n;
    in >> n;
    for (int i = 1; i<=n; i++)
    {
        in >> v[i];
        lst[i] = v[i];
    }
    int k = 0;
    sort(lst+1,lst+n+1);
    for (int i = 1; i<=n; i++)
        if (lst[i]!=lst[k])
            lst[++k] = lst[i];
    for (int i = 1; i<=n; i++)
        v[i] = lower_bound(lst+1,lst+k+1,v[i])-lst;
    int ans = INT_MAX;
    for (int i = 1; i<=n; i++)
    {
        viz[0] = i;
        for (int j = i; j<=n; j++)
        {
            if (viz[v[j]-1] == i && viz[v[j]]!=i)
            {
                viz[v[j]] = i;
                dp[v[j]] = j;
            }
        }
        if (viz[1] == i && viz[k] == i)
            ans = min(ans,dp[k]-dp[1]+1);
    }
    if (ans == INT_MAX)
        out << -1;
    else
        out << ans;
}