#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;cin >> n;
    int ans =0;
    vector<int>volgy(n);
    for(int i = 0;i < n;i++){cin >> volgy[i];}
    int l1=0,l2=-1;
    for(int i =1;i < n;i++){
        if (volgy[i] >= volgy[l1]){
            l2 = l1;l1 = i;
            ans = max(ans,abs(l1-l2));
            l2 = -1;
        }else if(volgy[i]> volgy[l2] || l2 == -1){
            l2 = i;
        }
        if(l2 != -1) ans = max(ans,abs(l1-l2));
    }
    if(ans < 3) cout << -1;
    else cout << ans;
}