#include <iostream>
#include <numeric>
#include <cmath>
#include <vector>

void solve() {
    int n;
    std::cin >> n;

    std::vector<int> xs(n);
    for (auto& x : xs) std::cin >> x;

    auto get = [&](int i) {
        return 0 <= i && i < n ? xs[i] : 0;
    };

    int ans = 100000;
    for (int c = 1; c <= 100; ++c) {
        int moved = 0, need = 0;

        int y = 0;
        bool peak = false;
        for (int i = 0;; ++i) {
            if (y == c) peak = true;

            y += (peak ? -1 : 1);
            if (i >= n && y < 0) break;
            y = std::max(y, 0);

            int x = get(i);

            if (x < y) {
                need += y - x;
            } else if (x > y) {
                moved += x - y;
            }
        }

        if (need > moved) continue;
        ans = std::min(ans, moved);
    }

    std::cout << ans << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}