#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000


int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);
	int N; cin >> N;
	int A[110];
	rep(i, N) cin >> A[i];
	int sum = 0;
	rep(i, N) sum += A[i];
	int cnt = 1;
	while (true) {
		int tmp = 0;
		rep(i, cnt - 1) {
			tmp += (i + 1) * 2;
		}
		tmp += cnt;
		if (tmp > sum) break;
		cnt++;
		
	}
	int ans = 100000;
	rep(i, cnt - 1) {
		rep(k, N - (i * 2)) {
			int B[110] = {};
			rep(j, i) {
				B[j + k] = j + 1;
			}
			B[i + k] = i + 1;
			rep(j, i) {
				B[j + i + 1 + k] = B[j + i + k] - 1;
			}
			int tmp1 = 0;
			int tmp2 = 0;
			rep(j, N) {
				//cout << B[j] << " ";
				if (A[j] < B[j]) tmp1 += B[j] - A[j];
				else if (A[j] > B[j]) tmp2 += A[j] - B[j];
			}
			//cout << endl;
			//cout << tmp1 << " " << tmp2 << endl;
			ans = min(ans, tmp2);
		}
		//rep(j, 10) cout << B[j] << " ";
		//cout << endl;

	}
	cout << ans << endl;

    return 0;
}