#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

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

int n, A[N], B[N], pos[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];

namespace BIT {
    int c[N];
    
    void fix(int x, int val = 1) {for (int i = x; i <= n; i += i & (-i)) c[i] += val;}

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

ll calc(int len) {
    ll res = 0;
    for (int i = 1; i <= len; i++) if (!pos) return inf;
    for (int i = 1; i <= len; i++) res += BIT::query(n) - BIT::query(pos[i]), BIT::fix(pos[i]);
    for (int i = 1; i <= len; i++) BIT::fix(pos[i], -1);
    return res;
}

bool geto(int o, int x) {return (x & 1) ^ o ^ 1;}

ll dp(int cur, int o)
{
	if (f[cur][o] < inf) return f[cur][o];
	if (!cur || !a[cur].h) 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++) a[i].h < 0 ? A[++totA] = a[i].p : B[++totB] = a[i].p;
	int len = cur - nxt + 1, cntA = 0, cntB = 0;
	for (int i = 1; i <= len; i++) geto(o, i) ? pos[i] = A[++cntA] : pos[i] = B[++cntB];
    ll f0 = inf, f1 = inf;
	if ((len & 1) != (cur & 1))
	{
		if (cntA == totA && cntB == totB)
		{
			ll s = calc(len);
			for (int i = 1; i <= len; i++) s += c[pos[i]][0];
			for (int i = len; i >= 0; i--) {
				geto(o, i) ? f0 = min(f0, s) : f1 = min(f1, s);
				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++) geto(o, i) ? pos[i] = A[++cntA] : pos[i] = B[++cntB];
			geto(o, len) ? pos[len] = B[++cntB] : pos[len] = A[++cntA];
			p = len - 1;
		}
		if (cntA == totA && cntB == totB) {
			ll s = calc(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--;
				}
			}
		}
	}
	return f[cur][o] = min(f[cur][o], min(f0 + dp(nxt - 1, 0), f1 + dp(nxt - 1, 1)));
}

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(BIT::c, 0, sizeof(BIT::c)), memset(f, 0x3f, sizeof(f));
    cout << (dp(n, 0) < inf ? dp(n, 0) : -1);
    return 0;
}