#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))
#define REPEAT(i, k, n)     for(int(i)=(k);(i)<((k)+(n));++(i))

int k[1000];
int l[1000];
int m[1000];

int main(){
    int N;
    cin >> N;
    REP(i,N) cin >> k[i];
    
    int minv = 1<<29;
    for(int i = 1; i < 1000; i += 2){
        memcpy(l, k, sizeof(k));
        memset(m,0,sizeof(m));

        for(int j = 0; j < i; j++){
            m[j] = j+1;
            if(j > i/2) m[j] = i-j;
        }

        int n = 0, p = 0;
        for(int j = 0; j < max(i,N); j++){
            if(l[j] > m[j]){
                n += l[j]-m[j];
            }
            if(l[j] < m[j]){
                p += m[j]-l[j];
            }
        }
        if(n < p) continue;
        minv = min(minv, n);
    }
    cout << minv << endl;

    return 0;
}