#include <iostream>
#include <bits/stdc++.h>
using ll = long long;
using namespace std;

int main()
{
    ll n; cin >> n;
    vector<int> v(n);
    for (ll i = 0; i < n; i++){
        cin >> v[i];
    }
    ll longest = 0, cur = 0, l = 0, ind = 0, flag = 1;
    for (ll i = 1; i < n; i++){
        cur++;
        if (v[i] <= v[l]) continue;
        else {
            flag = 0;
            if (longest < cur){
                longest = cur; ind = i-cur;
            }
            l = i; cur = 0;
        }
    }
//    if (longest < cur){
//        longest = cur; ind = n-cur;
//    }
    if (flag == 1) cout << -1;
    else cout << ind+1; //1-tol indexelsz;
    return 0;
}