#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

#define NMAX 5007

int p[NMAX];
vector < int > norm;
vector < int > :: iterator it;
int i,cu,j,N,u,sol;

int main()
{
freopen("secv.in","r",stdin);
freopen("secv.out","w",stdout);

scanf("%d",&N);

for (i=1;i<=N;++i)
{
    scanf("%d",&p[i]);
    norm.push_back(p[i]);
}

sort(norm.begin(),norm.end());
it=unique(norm.begin(),norm.end());
norm.resize(distance(norm.begin(),it));

for (i=1;i<=N;++i)
{
    p[i]=lower_bound(norm.begin(),norm.end(),p[i])-norm.begin()+1;
    u=max(u,p[i]);
}

for (i=1,sol=N+1;i<=N;++i)
{
    cu=0;

    for (j=i;j<=N && j-i+1<=sol;++j)
    {
        if (p[j]==cu+1) ++cu;
        if (cu==u) sol=j-i+1;
    }
}

if (sol==N+1) sol=-1;
printf("%d\n",sol);

return 0;
}