#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define RREP(i,s,e) for (int i = e-1; i >= s; i--)
#define rrep(i,n) RREP(i,0,n)
#define REP(i,s,e) for (int i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)

int main() {
    int n, sum, height, ans;
    cin >> n;
    int a[n];
    rep (i,n) cin >> a[i];
    sum = accumulate(a,a+n,0);
    height = sqrt(sum);
    ans = 0;
    rep (i,min(n,height*2 - 1))
        ans += max(0, a[i] - min(i+1,height*2 - 1 - i));
    REP (i,height*2 - 1,n)
        ans += a[i];
    cout << ans << endl;
    return 0;
}