#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];
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 , dr , med , k , lmin , q , w;
    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];
    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;
        }
    }
    k = cnt;
    cnt = 0;
    f[0] = 1;
    lmin = n + 1;
    st = 1;
    for(dr = 1;dr <= n;dr++){
      q = 1;
      while(v[dr] != 1)
        dr++;
      st = dr + 1;
      q++;
      while(st <= n && q <= k){
        st++;
        if(v[st] == q)
          q++;
      }
      if(q > k && st - dr + 1 < lmin){
        lmin = st - dr + 2;
      }
    }
    if(lmin != n + 1)
      printf("%d\n" , lmin);
    else
      printf("-1");
    return 0;
}