/* -*- 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];

/* 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 <= n; k += 2) {
    int sum = 0, hk = (k + 1) / 2;
    if (hk * hk > asum) break;
    for (int i = 0; i < n; i++) {
      int pai = (i >= k) ? 0 : (i >= hk) ? k - i : i + 1;
      //printf("%d,%d: %d\n", k, i, pai);
      if (as[i] > pai) sum += as[i] - pai;
    }
    if (minsum > sum) minsum = sum;
  }

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