#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int n;
    cin >> n;
    int a[n];
    int sum = 0;
    rep(i,n){
        cin >> a[i];
        sum += a[i];
    }

    int ans = 1001001001;

    srep(i,1,1000){
        if(i % 2 == 0)continue;
        int tmp = (i/2+1) * (i/2+1);
        if(sum < tmp)break;
        int cnt = 0;
        int b[1010] = {};
        rep(j,i/2+1){
            b[j] = j + 1;
            b[i-1-j] = j + 1;
        }
        rep(j,n){
            cnt += max(0, a[j] - b[j]);
        }
        ans = min(ans, cnt);

        /*
        rep(j,n)cout << b[j] << ' ';
        cout << endl << cnt << endl;
        */
    }

    cout << ans << endl;
    return 0;
}