#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 500'000 + 10,
MAX = 1'000'000'000'000'000;
int n;
int h[N];
struct BIT {
int bit[N];
inline void upd(int i, int x) {
for (; i <= n; i += i & -i) bit[i] += x;
}
inline int que(int i) {
int ret = 0;
for (; i; i -= i & -i) ret += bit[i];
return ret;
}
} T, Z;
int pref[N];
vector<int> position;
int32_t main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n;
for (int i = 1; i <= n; ++i) cin >> h[i];
int cntZero = 0, totalZero = 0;
for (int i = 1; i <= n; ++i) {
if (h[i]) continue;
position.push_back(i);
cntZero += 1;
totalZero += i - 1 - Z.que(i - 1);
Z.upd(i, 1);
}
const int sz = n - cntZero;
int answer = MAX;
for (int type = 1; type <= 2; ++type) {
memset(pref, 0, sizeof pref);
memset(T.bit, 0, sizeof T.bit);
deque<int> odd, even;
for (int i = 1; i <= n; ++i) {
if (!h[i]) continue;
auto& vt = (i ^ (h[i] == 1)) & 1 ? odd : even;
vt.push_back(i);
}
vector<int> sequence;
for (int i = 1; i < sz; ++i) {
auto& ret = pref[i];
ret = pref[i - 1];
auto& vt = i & 1 ? odd : even;
if (!vt.size()) { ret = MAX; continue; }
int pos = vt.front();
vt.pop_front();
ret += pos - 1 - T.que(pos - 1);
ret -= position.end() - upper_bound(position.begin(), position.end(), pos);
T.upd(pos, 1);
sequence.push_back(pos);
}
int total = totalZero;
if (type == 1) { //calculate total
auto& vt = (n ^ 1) & 1 ? odd : even;
if (!vt.size()) total = MAX;
else {
int pos = vt.front();
vt.pop_front();
total += pos - 1 - T.que(pos - 1) - Z.que(pos - 1);
sequence.push_back(pos);
}
} else if (sz) {
auto& ret = pref[sz];
ret = pref[sz - 1];
auto& vt = sz & 1 ? odd : even;
if (!vt.size()) ret = MAX;
else {
int pos = vt.front();
vt.pop_front();
ret += pos - 1 - T.que(pos - 1);
ret -= position.end() - upper_bound(position.begin(), position.end(), pos);
T.upd(pos, 1);
sequence.push_back(pos);
}
}
if ((int)sequence.size() == sz) {
if (type == 1) answer = min(answer, pref[sz - 1] + total);
else answer = min(answer, pref[sz] + total);
for (int i = (type == 1 ? sz - 2 : sz - 1); i >= 1; i -= 2) {
if (!(cntZero & 1)) swap(sequence[i - 1], sequence[i]);
T.upd(sequence[i - 1], -1);
T.upd(sequence[i], -1);
total += sequence[i - 1] - 1 - T.que(sequence[i - 1] - 1) - Z.que(sequence[i - 1] - 1);
T.upd(sequence[i - 1], 1);
total += sequence[i] - 1 - T.que(sequence[i] - 1) - Z.que(sequence[i] - 1);
T.upd(sequence[i], 1);
T.upd(sequence[i - 1], -1);
T.upd(sequence[i], -1);
answer = min(answer, pref[i - 1] + total);
}
}
}
cout << (answer == MAX ? -1 : answer) << "\n";
}
