#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

constexpr int N = 5e5 + 10;
constexpr ll inf = 0x3f3f3f3f3f3f3f3fll;

int n;
ll f[N][2], c[N][2];

struct Node {
    int h, p;

    bool operator<(const Node &rhs) const {
        if (abs(h) == abs(rhs.h)) return h == rhs.h ? p < rhs.p : h < rhs.h;
        return abs(h) < abs(rhs.h);
    }
} a[N];

ll dp(int cur, int o) {
    if (f[cur][o] != inf) return f[cur][o];
    if (!cur || !a[cur].h) return 0;
    if (a[cur].h * (o ? 1 : -1) <= 0) f[cur][o] = min(f[cur][o], c[cur][0] + dp(cur - 1, o ^ 1));
    if (a[cur].h * (((cur & 1) ^ o) ? -1 : 1) >= 0) f[cur][o] = min(f[cur][o], c[cur][1] + dp(cur - 1, o));
    return f[cur][o];
}

namespace BIT {
    int c[N];
    
    void fix(int x) {for (int i = x; i <= n; i += i & (-i)) c[i]++;}

    int query(int x) {int res = 0; for (int i = x; i; i -= i & (-i)) res += c[i]; return res;}
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(nullptr), cout.tie(nullptr);
    cin >> n; for (int i = 1; i <= n; i++) a[i].p = i, cin >> a[i].h;
    for (int i = 1; i <= n; i += 2) a[i].h = -a[i].h;
    sort(a + 1, a + n + 1); int j = 1;
    for (int i = 1; i <= n; i++) {
        while(abs(a[j].h) < abs(a[i].h)) BIT::fix(a[j++].p);
        c[a[i].p][0] = BIT::query(a[i].p - 1), c[a[i].p][1] = BIT::query(n) - BIT::query(a[i].p);
    }
    memset(f, 0x3f, sizeof(f));
    cout << (dp(n, 0) < inf ? dp(n, 0) : -1);
    return 0;
}