#include <bits/stdc++.h>
using namespace std;
using ll = long long;
// const ll MOD = 1e9+7;

#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()

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

    int n; cin >> n;
    vector<int> pos(n+1);
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
    	cin >> a[i];
    	pos[a[i]] = i;
    }
    
    int mn = INT_MAX;
    int start = 1;
    for (int i = 2; i <= n; i++) {
    	if (pos[i-1] > pos[i]) {
    		int x = start-1, y = n-i+1;
    		mn = min(mn, max(max(0, 2*x-1), 2*y));
    		start = i;
    	}
    }
    int x = start-1, y = 0;
    mn = min(mn, max(max(0, 2*x-1), 2*y));
    cout << mn << "\n";
    
    return 0;
}