#include <stdio.h>
#include <string.h>
#define N 500000
#define INF 0x3f3f3f3f3f3f3f3fLL
int abs_(int a) { return a > 0 ? a : -a; }
long long min(long long a, long long b) { return a < b ? a : b; }
int max(int a, int b) { return a > b ? a : b; }
unsigned int X = 12345;
int rand_() {
return (X *= 3) >> 1;
}
int aa[N];
int compare(int i, int j) {
int ai = abs_(aa[i]), aj = abs_(aa[j]);
if (ai != aj)
return aj - ai;
if (aa[i] != aa[j])
return aa[i] - aa[j];
return i - j;
}
void sort(int *ii, int l, int r) {
while (l < r) {
int i = l, j = l, k = r, i_ = ii[l + rand_() % (r - l)], tmp;
while (j < k) {
int c = compare(ii[j], i_);
if (c == 0)
j++;
else if (c < 0) {
tmp = ii[i], ii[i] = ii[j], ii[j] = tmp;
i++, j++;
} else {
k--;
tmp = ii[j], ii[j] = ii[k], ii[k] = tmp;
}
}
sort(ii, l, i);
l = k;
}
}
int ft[N];
void update(int i, int n) {
while (i < n) {
ft[i]++;
i |= i + 1;
}
}
int query(int i) {
int x = 0;
while (i >= 0) {
x += ft[i];
i &= i + 1, i--;
}
return x;
}
int main() {
static int ii[N], ii1[N], ii2[N], kkp1[N + 1], kkp2[N + 1], kkq1[N + 1], kkq2[N + 1];
static long long dp[2], dq[2], vvp[N + 1], vvq[N + 1];
int n, n0, n1, n2, h, h_, h1, r, s, i, k, k1, k2, l1, l2, a;
long long v, ans;
scanf("%d", &n);
for (i = 0; i < n; i++) {
scanf("%d", &aa[i]);
if (i % 2 != 0)
aa[i] = -aa[i];
}
for (i = 0; i < n; i++)
ii[i] = i;
sort(ii, 0, n);
memset(dp, 0x3f, sizeof dp), dp[0] = 0;
for (h = 0; h < n; h = h_) {
a = abs_(aa[ii[h]]);
if (a == 0)
break;
h_ = h, n1 = 0;
while (h_ < n && aa[i = ii[h_]] == -a)
ii1[n1++] = i - query(i), h_++;
n2 = 0;
while (h_ < n && aa[i = ii[h_]] == a)
ii2[n2++] = i - query(i), h_++;
n0 = n - h_;
for (h1 = h; h1 < h_; h1++)
update(ii[h1], n);
memset(dq, 0x3f, sizeof dq);
for (r = 0; r < 2; r++) {
if (dp[r] == INF)
continue;
kkp1[0] = k1 = 0, kkp2[0] = k2 = 0, vvp[0] = v = 0;
for (k = 1, l1 = 0, l2 = 0; k <= n1 + n2; k++) {
if ((k - 1) % 2 == r) {
if (k1 < n1) {
i = ii1[k1];
while (l2 < n2 && ii2[l2] < i)
l2++;
v += i - k1 - min(l2, k2);
}
k1++;
} else {
if (k2 < n2) {
i = ii2[k2];
while (l1 < n1 && ii1[l1] < i)
l1++;
v += i - k2 - min(l1, k1);
}
k2++;
}
kkp1[k] = k1, kkp2[k] = k2, vvp[k] = v;
}
kkq1[n1 + n2] = k1 = n1, kkq2[n1 + n2] = k2 = n2, vvq[n1 + n2] = v = 0;
for (k = n1 + n2 - 1, l1 = n1, l2 = n2; k >= 0; k--) {
if ((n0 + k) % 2 != r) {
k1--;
if (k1 >= 0) {
i = ii1[k1];
while (l2 > 0 && ii2[l2 - 1] >= i)
l2--;
v += n0 - (i - k1 - l2) + max(l2 - k2, 0);
}
} else {
k2--;
if (k2 >= 0) {
i = ii2[k2];
while (l1 > 0 && ii1[l1 - 1] >= i)
l1--;
v += n0 - (i - k2 - l1) + max(l1 - k1, 0);
}
}
kkq1[k] = k1, kkq2[k] = k2, vvq[k] = v;
}
for (k = 0; k <= n1 + n2; k++)
if (kkp1[k] == kkq1[k] && kkp2[k] == kkq2[k]) {
s = (r + k) % 2;
dq[s] = min(dq[s], dp[r] + vvp[k] + vvq[k]);
}
}
memcpy(dp, dq, sizeof dq);
}
ans = min(dp[0], dp[1]);
if (ans == INF)
ans = -1;
printf("%lld\n", ans);
return 0;
}
