import java.util.*;

class Main {
        public static void main(String args[]) {
                try (Scanner sc = new Scanner(System.in)) {
                        int N = sc.nextInt();
                        int[] A = new int[N];
                        int sum = 0;
                        for (int i = 0; i < N; i++) {
                                A[i] = sc.nextInt();
                                sum += A[i];
                        }
                        int ans = 1 << 29;
                        for (int i = 1; i * i <= sum; i++) {
                                int count = 0;
                                int stock = 0;
                                for (int j = 0; j < N; j++) {
                                        int x;
                                        if (j >= i) {
                                                x = i * 2 - j - 1;
                                        } else {
                                                x = j + 1;
                                        }
                                        if (x <= 0) {
                                                x = 0;
                                        }
                                        count += Math.abs(A[j] - x);
                                        stock += A[j] - x;
                                }
                                ans = Math.min((count + stock) / 2, ans);
                        }
                        System.out.println(ans);
                }
        }
}