import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        int total = 0;
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
            total += arr[i];
        }
        int max = (int)(Math.sqrt(total));
        int min = Integer.MAX_VALUE;
        for (int i = 1; i <= max; i++) {
            int count = 0;
            int sum = 0;
            for (int j = 0; j < n; j++) {
                if (j < i) {
                    count++;
                } else {
                    count--;
                    if (count < 0) {
                        count = 0;
                    }
                }
                sum += Math.max(0, arr[j] - count);
            }
            min = Math.min(sum, min);
        }
        System.out.println(min);
    }
}