#include <iostream>
#include <math.h>
#include <vector>
#include <array>
#include <algorithm>
#include <queue>
#include <numeric>
#include <map>
#include <set>

using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define SUM(a) accumulate(ALL(a), 0)
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) //printf(__VA_ARGS__)

typedef pair<int, int> pos;
int pos::*x = &pos::first;
int pos::*y = &pos::second;

int dxy[] = {0, 1, 0, -1, 0};

/*================================*/

int N;
vector<int> A;

signed main()
{
    
    cin >> N;
    A = vector<int>(100);
    REP(i,N) cin >> A[i];
    int total = SUM(A);
    
    int maxline = (int)sqrt(total) * 2 -1;
    out("max %lld\n", maxline);
    
    int minc = 20000;
    RREP(i,maxline+1) {
        if (i % 2 == 0) continue;
        int cnt = 0;
        REP(j,100) {
            int target;
            if (j <= (i + 1)/2-1) {
                target = j + 1;
            } else {
                target = max(i - j, (int)0);
            }
            cnt += max((int)(A[j] - target), (int)0);
        }
        out("%lld: %lld\n", i, cnt);
        minc = min(minc, cnt);
    }
    
    cout << minc << endl;
    
    return 0;
}