#include <bits/stdc++.h>

using namespace std;
using i64 = long long;

#define rep(i, l, r) for (int i = (l); i < (r); ++i)
#define per(i, l, r) for (int i = (r - 1); i >= (l); --i)
#define ALL(x) (x).begin(), (x).end()

class SegTree {
    int n, internalSize;
    vector<int> data;

  public:
    SegTree(int n_) : n(n_) {
        internalSize = 1;
        while (internalSize < n) internalSize *= 2;
        data.assign(2 * internalSize, 0);
    }

    void set(int i, int v) {
        i += internalSize;
        data[i] = v;
        while (i != 1) {
            i /= 2;
            data[i] = data[2 * i] + data[2 * i + 1];
        }
    }

    int fold(int l, int r) {
        int ret = 0;
        for (l += internalSize, r += internalSize; l < r; l /= 2, r /= 2) {
            if (l & 1) ret += data[l++];
            if (r & 1) ret += data[--r];
        }
        return ret;
    }
};

int main() {
    int N;
    cin >> N;
    vector<i64> H(N);
    for (auto &e : H) cin >> e;

    priority_queue<pair<int, int>> pq;
    rep (i, 0, N) pq.push({abs(H[i]), i});
    SegTree seg(N);
    rep (i, 0, N) seg.set(i, 1);
    i64 ans = 0;
    while (not pq.empty()) {
        const auto [val, i] = pq.top();
        pq.pop();
        seg.set(i, 0);
        const auto a = seg.fold(0, i), b = seg.fold(i + 1, N);

        int v = 1 << 30;
        if (H[i] >= 0 and a % 2 == 1) v = min(v, a);
        if (H[i] <= 0 and a % 2 == 0) v = min(v, a);
        if (H[i] >= 0 and b % 2 == 0) v = min(v, b);
        if (H[i] <= 0 and b % 2 == 1) v = min(v, b);
        cerr << v << endl;
        if (v == (1 << 30)) {
            ans = -1;
            break;
        }
        ans += v;
    }
    cout << ans << endl;
}