#include<bits/stdc++.h>

typedef long long ll;
using namespace std;
const int N = 1e5 + 10;
int n;

void solve() {
    cin >> n;
    vector<int> a(n + 1, 0);
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    int ans = 0;
    for (int i = 1; i <= n;) {
        int j = i;
        while (j + 1 <= n && a[j + 1] > a[j]) {
            j++;
        }
        int z = 1;
        int len = 1;
        while (j + z <= n && j - z >= 1 && a[j + z] == a[j - z]) {
            z++;
            len += 2;
        }
        ans = max(ans, len);
        i = j + max(1, z - 1);
    }
    if (ans == 1)cout << -1;
    else cout << ans;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int _ = 1;
//    cin >> _;
    for (int o = 1; o <= _; o++) solve();

    return 0;
}
/*

1
4
4 5 7 9

*/