#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;


int main(){
  int N, tmp;
  vector<int> v;
  cin >> N;
  int allv = 0;
  rep(i,N){
    cin >> tmp;
    v.push_back(tmp);
    allv += tmp;
  }

  int ret = 100000000;
  for(int i=1; i<=2*N; i+=2){
    int x = 1;
    vector<int> w;
    int allw = 0;
    rep(j,i){
      w.push_back(x);
      allw += x;
      if(j<i/2) x++;
      else x--;
    }
    if(allw>allv) break;
      
    int sum = 0;
    rep(j,w.size()){
      if(j<v.size() && v[j] > w[j]) sum += v[j]-w[j];
    }
    REP(j,w.size(),N) sum += v[j];
    //cout << w.size() << " " << sum << endl;
    ret = min(ret, sum);
  }

  cout << ret << endl;
  return 0;
}