#include <cstring>
#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <queue>
#include <algorithm>
#include <stack>

int N;
int A[128];
int total;

int diff(int h) {
  if( total < h * h ) return 100000;
  int target[128];
  for(int i = 0; i < h; ++i) {
    target[i] = i + 1;
  }
  for(int i = h; i < 2 * h - 1; ++i) {
    target[i] = 2 * h - i - 1; 
  }
  int res = 0;
  for(int i = 0; i < 2 * h - 1; ++i) {
    res += std::max(0, (A[i] - target[i]));
  }
  for(int i = 2 * h - 1; i < 128; ++i) {
    res += A[i];
  }
  if( res < 0 ) res = 100000;
  //printf("%d : %d\n", h, res);
  return res;
}

int main() {
  std::cin >> N;
  for(int i = 0; i < N; ++i) std::cin >> A[i];

  for(int i = 0; i < N; ++i) total += A[i];

  int res = 100000;
  for(int i = 1; i < 50; ++i) {
    res = std::min(res, diff(i));
  }

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