#include <fstream>
#include <string>
#include <stdio.h>
#include <vector>
#include <algorithm>
#include <math.h>
#include <set>
#include <map>

using namespace std;

#ifdef DEBUG
string name = "data";
#else
string name = "secv";
#endif

ifstream fin(name + ".in");
ofstream fout(name + ".out");

int main() {
    
    int n;
    
    fin >> n;
    
    int a[5005];
    pair<int, int> best[5005];
    map<int, int> p;
    set<int> used;
    
    for (int i = 0; i < n; ++i) {
        fin >> a[i];
        used.insert(a[i]);
    }
    
    int last = -1;
    
    int biggest = -1;
    
    for (auto x: used) {
        p[x] = last;
        last = x;
        biggest = max(biggest, x);
    }
    
    for (int i = 0; i < n; ++i) {
        if (p[a[i]] == -1) {
            best[i] = {i, 1};
            continue;
        }
        
        for (int j = i - 1; j >= 0; --j) {
            if (a[j] == p[a[i]] && best[j].second > 0) {
                best[i] = {i, best[j].second + i - j};
                break;
            }
        }
    }
    
    int res = 432414;
    bool found = false;

    for (int i = 0; i < n; ++i) {
        if (a[i] == biggest && best[i].second > 0) {
            res = min(res, best[i].second);
            found = true;
        }
    }
    
    if (found) {
        fout << res;
    } else {
        fout << "-1";
    }
    
    return 0;
}