import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int A[] = new int[101];
		Arrays.fill(A, 0);
		// 1オリジン
		for(int i = 1; i <= N; i++) {
			A[i] = scan.nextInt();
		}

		scan.close();

		int sum = 0;
		for(int i = 1; i <= N; i++) {
			sum += A[i];
		}
		int n = 1;
		int cost = 0;
		for(int i = 1; i < 100; i++) {
			if(sum == i * i) {
				n = i;
				break;
			}else if(sum < i * i) {
				n = i - 1;
				break;
			}
		}
		//cost = sum - n * n;
		cost = 0;

		for(int i = 1; i <= 2 * n - 1; i++) {
			if(i <= n) {
				if(A[i] >= i) {
					cost += i;
				}else {
					cost += A[i];
				}
			}else {
				int t = 2 * n - i;
				if(A[i] >= t) {
					cost += t;
				}else {
					cost += A[i];
				}
			}
		}

		int ans = sum - cost;
		System.out.println(ans);
	}
}