#include <bits/stdc++.h>
#define rep(i, l, r) for(int i = (l); i <= (r); i++)
#define per(i, r, l) for(int i = (r); i >= (l); i--)
#define mem(a, b) memset(a, b, sizeof a)
#define For(i, l, r) for(int i = (l), i##e = (r); i < i##e; i++)
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define SZ(x) int((x).size())

using namespace std;
using ll = long long;

template<class T> inline T& cmin(T& a, const T& b) { if(b < a) a = b; return a; }
template<class T> inline T& cmax(T& a, const T& b) { if(a < b) a = b; return a; }
template<class... Args> void print(Args&&... args) {
    ((cout << args << ' '), ...);
}
template<class... Args> void println(Args&&... args) {
    print(args...), cout << endl;
}

const int N = 5e5 + 8;
const ll inf = 0x3f3f3f3f3f3f3f3f;

int n, h[N];
pair<int, int> a[N];
ll dp[N][2];
int c[N];

inline void add(int i) {
    for(; i <= n; i += i & -i) c[i]++;
}
inline int sum(int i) {
    int s = 0;
    for(; i; i &= i - 1) s += c[i];
    return s;
}
int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin >> n;
    rep(i, 1, n) cin >> h[i];
    for(int i = 2; i <= n; i += 2) h[i] = -h[i];
    rep(i, 1, n) a[i] = {h[i], i};
    sort(a + 1, a + n + 1, [](auto a, auto b) {
        return abs(a.first) < abs(b.first);
    });
    rep(i, 1, n) {
        auto [v, p] = a[i];
        int L = sum(p), R = i - 1 - L;
        add(p);
        bool flag[2] = {v <= 0, v >= 0};
        dp[i][0] = dp[i][1] = inf;
        rep(j, 0, 1) {
            if(flag[j]) cmin(dp[i][!j], dp[i - 1][j] + L);
            if(flag[j ^ (~i & 1)]) cmin(dp[i][j], dp[i - 1][j] + R);
        }
    }
    cout << (dp[n][1] == inf ? -1 : dp[n][1]) << '\n';
}