#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
constexpr ll inf = 4.5e18;
int n;
struct node
{
	int p, h;
	bool operator<(const node &y) const
	{
		if (abs(h) != abs(y.h))
			return abs(h) < abs(y.h);
		if (h != y.h)
			return h < y.h;
		return p < y.p;
	}
} a[1000005];
struct BIT
{
	int tree[1000005];
	void clear()
	{
		memset(tree, 0, sizeof(tree));
		return;
	}
	void add(int p, int h)
	{
		while (p <= n)
			tree[p] += h, p += (p & (-p));
		return;
	}
	int ask(int p)
	{
		int ans = 0;
		while (p)
			ans += tree[p], p -= (p & (-p));
		return ans;
	}
} bit;
ll c[1000005][2];
ll f[1000005][2];
int A[1000005], B[1000005];
int pos[1000005];
ll ask(int len)
{
	ll ans = 0;
	for (int i = 1; i <= len; i++)
		if (pos[i] == 0)
			return inf;
	for (int i = 1; i <= len; i++)
	{
		ans += bit.ask(n) - bit.ask(pos[i]);
		bit.add(pos[i], 1);
	}
	for (int i = 1; i <= len; i++)
		bit.add(pos[i], -1);
	return ans;
}
int geto(int o, int x)
{
	return (x & 1) ^ 1 ^ o;
}
ll dfs(int cur, int o)
{
	if (f[cur][o] < inf)
		return f[cur][o];
	if (cur == 0)
		return 0;
	if (a[cur].h == 0)
		return 0;
	int nxt = cur; while (nxt > 1 && abs(a[nxt - 1].h) == abs(a[cur].h)) nxt--;
	int totA = 0, totB = 0;
	for (int i = nxt; i <= cur; i++)
		if (a[i].h < 0)
			A[++totA] = a[i].p;
		else
			B[++totB] = a[i].p;
	int len = cur - nxt + 1;
	ll f0 = inf, f1 = inf;
	int cntA = 0, cntB = 0;
	for (int i = 1; i <= len; i++)
		if (geto(o, i) == 1)
			pos[i] = A[++cntA];
		else
			pos[i] = B[++cntB];
	if ((len & 1) != (cur & 1))
	{
		if (cntA == totA && cntB == totB)
		{
			ll s = ask(len);
			for (int i = 1; i <= len; i++)
				s += c[pos[i]][0];
			for (int i = len; i >= 0; i--)
			{
				if (geto(o, i + 1) == 0)
					f0 = min(f0, s);
				else
					f1 = min(f1, s);
				if (i == 0)
					break;
				s -= c[pos[i]][0], s += c[pos[i]][1];
			}
		}
	}
	else
	{
		int p = len;
		if (cntA != totA || cntB != totB)
		{
			cntA = 0, cntB = 0;
			for (int i = 1; i < len; i++)
				if (geto(o, i) == 1)
					pos[i] = A[++cntA];
				else
					pos[i] = B[++cntB];
			if (geto(o, len) == 0)
				pos[len] = A[++cntA];
			else
				pos[len] = B[++cntB];
			p = len - 1;
		}
		if (cntA == totA && cntB == totB)
		{
			ll s = ask(len);
			for (int i = 1; i <= p; i++)
				s += c[pos[i]][0];
			for (int i = p + 1; i <= len; i++)
				s += c[pos[i]][1];
			for (int i = p; i >= 0; i -= 2)
			{
				if (geto(o, i + 1) == 0)
					f0 = min(f0, s);
				else
					f1 = min(f1, s);
				if (i >= 2)
				{
					s -= c[pos[i - 1]][0], s += c[pos[i - 1]][1];
					s -= c[pos[i]][0], s += c[pos[i]][1];
					if (pos[i - 1] < pos[i])
						s++;
					else
						s--;
				}
			}
		}
	}
	ll ans = inf;
	ans = min(ans, f0 + dfs(nxt - 1, 0));
	ans = min(ans, f1 + dfs(nxt - 1, 1));
	return f[cur][o] = ans;
}
int main()
{
	scanf("%d", &n);
	for (int i = 1; i <= n; i++)
	{
		a[i].p = i;
		scanf("%d", &a[i].h);
		if (i & 1)
			a[i].h = -a[i].h;
	}
	sort(a + 1, a + 1 + n);
	int j = 1;
	for (int i = 1; i <= n; i++)
	{
		while (abs(a[j].h) < abs(a[i].h))
			bit.add(a[j].p, 1), j++;
		c[a[i].p][0] = bit.ask(a[i].p - 1);
		c[a[i].p][1] = bit.ask(n) - bit.ask(a[i].p);
	}
	bit.clear();
	memset(f, 0x3f, sizeof(f));
	ll ans = dfs(n, 0);
	if (ans == inf)
		ans = -1;
	cout << ans << endl;
	return 0;
}