#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int main() {
    
    int N;
    cin >> N;
    vector<int> A(N);
    int s = 0;
    for ( int i = 0; i < N; i++ ) {
        cin >> A[i];
        s += A[i];
    }
    
    int ans = INT_MAX;
    for ( int i = 1; ((i+1)/2)*((i+1)/2) <= s; i += 2 ) {
        
        int x = 0;
        for ( int j = 0; j < i; j++ ) {
            int y = (i+1)/2 - abs( i/2 - j );
            
            x += max( 0, y - ( (j < N) ? A[j] : 0 ) );
        
        }
        // cout << i << " " << x << endl;
        
        x += s-(((i+1)/2)*((i+1)/2));
        
        // cout << i << " " << x << endl;
        
        ans = min( ans, x );
    }
    
    cout << ans << endl;
    
    return 0;
}