#define _USE_MATH_DEFINES

#include <iostream>
#include <iomanip>

#include <algorithm>
#include <cmath>

#include <string>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>

/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////

int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    //cout << setprecision(6);//
	
	int N;
	cin>>N;
	int A[200];
	int Amax=0;
	rep(i,N){
		cin>>A[i];
		Amax += A[i];
	}
	for(int i=N;i<200;++i){
		A[i] = 0;
	}
	///////
	//N^2
	int ans = -1;
	int tans;
	int ooi=0;
	int suk=0;
	int use=0;
	for(int i=0;i*i<=Amax;++i){
		tans = 0;
		ooi=0;
		suk=0;
		use=0;
		for(int k = 1; k <= 2*i-1 ;++k){
			use +=A[k-1];
			if ( k <= i){
				if( A[k-1]>k){
					ooi += A[k-1]-k;
				}
				else{
					suk += k-A[k-1];
				}
			}else{//2*i-k
				if( A[k-1]>2*i-k){
					ooi += A[k-1] -(2*i-k);
				}
				else{
					suk += (2*i-k) - A[k-1];
				}
			}
		}
		if( suk > ooi){
			tans = suk;
			suk = suk-ooi;
		}else{
			tans = ooi;
			suk = 0;
		}
		//残り
		tans += Amax - use - suk;
		if(ans == -1 || ans > tans){
			ans = tans;
		}
	}
	P(ans);
	return 0;
}