#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define flt double
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()

mt19937 rnd(234);
const ll inf = 1e17;

int n;
vector<ll> h;

ll solve_abs_1() {
    vector<int> a(n + 2);
    a[0] = 0;
    a[n + 1] = 1;
    for (int i = 0; i < n; i += 1) {
        if (h[i] < 0) {
            a[i + 1] = 0;
        } else {
            a[i + 1] = 1;
        }
    }
    vector<int> d(n + 1);
    for (int i = 0; i <= n; i += 1) {
        d[i] = (a[i] ^ a[i + 1]);
    }
    vector<int> stck;
    vector<ll> bebra(n + 1, inf);
    ll sm = 0;
    for (int i = 0; i <= n; i += 1) {
        if (d[i]) {
            if (!stck.empty() && stck.back() % 2 == i % 2) {
                sm += (i - stck.back()) / 2;
                stck.pop_back();
            } else {
                stck.push_back(i);
            }
            if (stck.size() == 1) {
                bebra[i] = sm;
            }
        }
    }
    ll rs = inf;
    stck.clear();
    sm = 0;
    for (int i = n; i >= 0; i -= 1) {
        if (stck.empty()) {
            rs = min(rs, sm + bebra[i]);
        }
        if (d[i]) {
            if (!stck.empty() && stck.back() % 2 == i % 2) {
                sm += (stck.back() - i) / 2;
                stck.pop_back();
            } else {
                stck.push_back(i);
            }
        }
    }
    if (rs > inf / 4) {
        return -1;
    }
    return rs;
}

int32_t main() {
    if (1) {
        ios::sync_with_stdio(0);
        cin.tie(0);
        cout.tie(0);
    }
    cin >> n;
    h.resize(n);
    for (int i = 0; i < n; i += 1) {
        cin >> h[i];
    }
    cout << solve_abs_1() << "\n";
    return 0;
}

/*
4
1 -1 1 -1

4
1 1 -1 -1

*/