#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

int main() {
	int n;

	cin >> n;
	vector<int> a(2 * n - 1, 0);
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}
	vector<int> b(2 * n -  1, 0);

	int ans = 1e9;
	for (int center = 0; center < n; center++) {
		fill(b.begin(), b.end(), 0);
		int i;
		for (i = 0; i <= center; i++) {
			b[i]  = i + 1;
		}
		for ( ; b[i - 1] > 0; i++) {
			b[i] = b[i - 1] - 1;
		}

		int more = 0;
		int less = 0;

		for (int j = 0; j < a.size(); j++) {
			int diff = a[j] - b[j];

			if (diff > 0) {
				more += diff;
			} else {
				less +=  -diff;
			}

		}
		if (more >= less) {
			ans = min(ans, more);
		}
	}
	cout << ans << endl;
	return 0;
}