#include <cstdio>
#include <queue>
#include <algorithm>
using namespace std;
const int NMAX = 5000;
int v[NMAX + 5] , t[NMAX + 5] , p[NMAX + 5] , f[NMAX + 5] , poz[NMAX + 5];
typedef pair<int,int> ii;
deque <ii> q;
int main()
{
    freopen("secv.in" , "r" , stdin);
    freopen("secv.out" , "w" , stdout);
    int n , i , cnt , st , med , k , lmin , m , val , j , dr;
    scanf("%d" , &n);
    for(i = 1 ; i <= n ; i ++)
        scanf("%d" , &v[i]) , t[i] = v[i];
    sort(t + 1 , t + n + 1);
    cnt = 0;
    v[n + 1] = 2000000001;
    for(i = 1 ; i <= n ; i ++)
        if(t[i] != t[i + 1])
            p[++ cnt] = t[i];
    m = 0;
    for(i = 1 ; i <= n ; i ++)
    {
        st = 1;
        dr = cnt;
        while(st <= dr)
        {
            med = (st + dr) / 2;
            if(p[med] == v[i])
            {
                v[i] = med;
                break;
            }
            else if(p[med] < v[i])
                st = med + 1;
            else
                dr = med - 1;
        }
        if(v[i] == 1)
             poz[++ m] = i;
    }
    k = cnt;
    lmin = n + 1;
    for(i = 1 ; i <= m ; i ++)
    {
        st = poz[i];
        val = 2;
        for(j = st ; j <= n ; j ++)
        {
          if(v[j] == val)
            val ++;
          if(val == k + 1)
          {
              if(j - st + 1 < lmin)
                lmin = j - st + 1;
              break;
          }
        }
    }
    if(lmin < n + 1)
        printf("%d\n" , lmin);
    else
        printf("-1\n");
    return 0;
}