//#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <unordered_map>
using namespace std;
ifstream cin("secv.in");
ofstream cout("secv.out");
unordered_map <int,int> um;
vector <int> f[5005];
int v[5005],norm[5005],d[5005],nex[5005],gigel[5005];
void solve(int i,int total){
    if(d[i]!=-2)
        return;
    if(v[i]==total){
        d[i]=i;
        return;
    }
    if(nex[i]==-1){
        d[i]=-1;
        return;
    }
    solve(nex[i],total);
    d[i]=d[nex[i]];
}
int main()
{
    int n;
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>v[i];
        norm[i]=v[i];
    }
    sort(norm+1,norm+n+1);
    int cur=0;
    norm[0]=-1;
    for(int i=1;i<=n;i++){
        if(norm[i]!=norm[i-1]){
            cur++;
            um[norm[i]]=cur;
        }
    }
    for(int i=1;i<=n;i++){
        v[i]=um[v[i]];
    }
    for(int i=1;i<=n;i++){
        f[v[i]].push_back(i);
    }
    for(int i=1;i<=cur;i++){
        gigel[i]=0;
    }
    for(int i=1;i<=n;i++){
        if(v[i]==cur){
            nex[i]=i;
            gigel[v[i]]++;
            continue;
        }
        if(gigel[v[i]+1]>=f[v[i]+1].size()){
            nex[i]=-1;
        }
        else
        nex[i]=f[v[i]+1][gigel[v[i]+1]];
        gigel[v[i]]++;
    }
    for(int i=1;i<=n;i++){
        d[i]=-2;
        //cout<<nex[i]<<" ";
    }
    //cout<<"\n";
    for(int i=1;i<=n;i++){
        solve(i,cur);
        //cout<<d[i]<<" ";
    }
    int sol=999999;
    for(int i=1;i<=n;i++){
        if(v[i]==1 and d[i]!=-1){
            sol=min(sol,d[i]-i+1);
        }
    }
    if(sol==999999)
        sol=-1;
    cout<<sol;
    return 0;
}