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

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int N; cin >> N;
    vector<int> A(N);
    rep(i,N) cin >> A[i];

    int MAX_L = 201;
    auto gen = [](int LEN) {
        vector<int> B;
        for(int i = 1; i <= LEN; i++) B.push_back(i);
        for(int i = LEN - 1; i >= 1; i--) B.push_back(i);
        return B;
    };

    auto calc = [](vector<int> A, vector<int> B) {
        if(accumulate(A.begin(), A.end(), 0) < accumulate(B.begin(), B.end(), 0)) {
            return int(1e9);
        } else {
            while(A.size() < B.size()) A.push_back(0);
            while(A.size() > B.size()) B.push_back(0);
            int N = A.size();
            int cost = 0;
            rep(i,N) if(A[i] > B[i]) cost += A[i] - B[i];
            return cost;
        }
    };

    int ans = 1e9;
    for(int i = 1; i <= MAX_L; i++) ans = min(ans, calc(A, gen(i)));
    cout << ans << endl;
}