// #pragma GCC optimize("O3")
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include <map>
#include <set>
#include <queue>
#include <vector>
#include <cstdio>
#include <cassert>
#include <iostream>
#include <algorithm>
using namespace std;

#define PB push_back
#define int long long
#define ll long long
#define vi vector<int>
#define siz(a) ((int) ((a).size()))
#define rep(i, a, b) for (int i = (a); i <= (b); ++i)
#define per(i, a, b) for (int i = (a); i >= (b); --i)
void print(vi n) { rep(i, 0, siz(n) - 1) cerr << n[i] << " \n"[i == siz(n) - 1]; }

const int N = 5e5, inf = 1e18;
int a, s[N + 5], w1[N + 5], w2[N + 5], L[N + 5], R[N + 5], q[N + 5], top;
vi p[N + 5][2];

void add(int *w, int n, int m) {
	w[a + 1] += m;
	for(; n <= a; n += n & -n) w[n] += m;
}
int ask(int *w, int n) {
	int res = 0;
	for(; n; n -= n & -n) res += w[n];
	return res;
}
int up(int *w, int n) {
	return w[a + 1] - ask(w, n);
}
int low(int *w, int n) {
	return ask(w, n - 1);
}

signed main() {
	// freopen(".in", "r", stdin);
	// freopen(".out", "w", stdout);
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	cin >> a;
	rep(i, 1, a) cin >> s[i], q[++top] = abs(s[i]);
	sort(q + 1, q + top + 1);
	top = unique(q + 1, q + top + 1) - q - 1;
	rep(i, 1, a) if(s[i] != 0) {
		int x = lower_bound(q + 1, q + top + 1, abs(s[i])) - q;
		// cout << ((abs(s[i]) != s[i]) == (i & 1)) << endl;
		p[x][(abs(s[i]) != s[i]) == (i & 1)].PB(i);
	}
	rep(i, 1, a) add(w1, i, 1);
	int f[2] = {inf, 0}, siz = a;
	per(i, top, 1) {
		if(q[i] == 0) break;

		sort(p[i][0].begin(), p[i][0].end());
		sort(p[i][1].begin(), p[i][1].end());
		int g[2] = {inf, inf}, b = siz(p[i][0]) + siz(p[i][1]);
		for(int x : p[i][0]) add(w1, x, -1);
		for(int x : p[i][1]) add(w1, x, -1);
		rep(j, 1, b) L[j] = R[j] = inf;
		rep(x, 0, 1) {
			int y = x ^ (siz & 1);
			vi::iterator j[2] = {p[i][0].begin(), p[i][1].begin()};
			for(int o = x, siz = 1; ; ++siz, ++j[o], o ^= 1) {
				if(j[o] == p[i][o].end()) break;
				L[siz] = L[siz - 1] + up(w2, *j[o]) + low(w1, *j[o]);
				add(w2, *j[o], 1);
			}
			for(; j[0] != p[i][0].end(); add(w2, *j[0], 1), ++j[0]);
			for(; j[1] != p[i][1].end(); add(w2, *j[1], 1), ++j[1]);
			for(int o = y, siz = 1; ; ++siz, o ^= 1) {
				// cout << *j[o] << ' ' << j[o] - p[i][o].end() << endl;
				if(j[o] == p[i][o].begin()) break;
				--j[o];
				add(w2, *j[o], -1);
				R[siz] = R[siz - 1] + up(w2, *j[o]) + up(w1, *j[o]);
			}
			for(; j[0] != p[i][0].begin(); add(w2, *(--j[0]), -1));
			for(; j[1] != p[i][1].begin(); add(w2, *(--j[1]), -1));
			// if(q[i] == 2) cout << L[0] << ' ' << R[2] << ' ' << f[x] << ' ' << x << ' ' << y << endl;
			rep(j, 0, b) g[x ^ (j & 1)] = min(g[x ^ (j & 1)], L[j] + R[b - j] + f[x]);
			// return 0;
		}
		swap(f, g);
		siz -= b;
		// cout << f[0] << ' ' << f[1] << endl;
	}
	int ans = min(f[0], f[1]);
	ans > a * (a - 1) / 2 ? cout << -1 : cout << ans;
	return cerr << endl << 1.0 * clock() / CLOCKS_PER_SEC << endl, 0;
}