/* -*- coding: utf-8 -*-
 *
 * 77.cc: No.77 レンガのピラミッド - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100;
const int INF = 1 << 30;

/* typedef */

/* global variables */

int as[MAX_N * 2];

/* subroutines */

/* main */

int main() {
  int n;
  cin >> n;

  int asum = 0;
  for (int i = 0; i < n; i++) {
    cin >> as[i];
    asum += as[i];
  }

  int minsum = INF;
  
  for (int k = 1;; k += 2) {
    int hk = (k + 1) / 2;
    if (hk * hk > asum) break;

    int maxi = max(n, k);
    for (int i = 0; i + k <= maxi; i++) {
      int sum = 0;
      for (int j = 0; j < n; j++) {
	int j0 = j - i;
	int paj = (j0 < 0 || j0 >= k) ? 0 : (j0 >= hk) ? k - j0 : j0 + 1;
	//printf("%d,%d: %d\n", k, i, pai);
	if (as[j] > paj) sum += as[j] - paj;
      }
      if (minsum > sum) minsum = sum;
    }
  }

  printf("%d\n", minsum);
  return 0;
}