#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];
int pref[N];
int32_t main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n;
for (int i = 1; i <= n; ++i) cin >> h[i];
int answer = MAX;
{ // the number of 1 is odd
deque<int> odd, even;
for (int i = 1; i <= n; ++i) {
auto& vt = (i ^ (h[i] == 1)) & 1 ? odd : even;
vt.push_back(i);
}
vector<int> sequence;
for (int i = 1; i < n; ++i) {
auto& ret = pref[i];
ret = pref[i - 1];
auto& vt = i & 1 ? odd : even;
if (!vt.size()) { ret = MAX; continue; }
sequence.push_back(vt.front());
ret += max(0ll, i - vt.front());
vt.pop_front();
}
if (pref[n - 1] < MAX) {
answer = min(answer, pref[n - 1]);
int total = 0;
{ // i == n
int i = n;
auto& ret = pref[i];
ret = pref[i - 1];
auto& vt = (i ^ 1) & 1 ? odd : even;
if (!vt.size()) ret = MAX;
sequence.push_back(vt.front());
ret += max(0ll, i - vt.front());
total += max(0ll, i - vt.front());
vt.pop_front();
}
for (int i = n - 2; i >= 1; i -= 2) {
swap(sequence[i - 1], sequence[i]);
total += max(0ll, i - sequence[i - 1]);
total += max(0ll, i + 1 - sequence[i]);
answer = min(answer, pref[i - 1] + total);
}
}
}
{ // the number of 1 is even
deque<int> odd, even;
for (int i = 1; i <= n; ++i) {
auto& vt = (i ^ (h[i] == 1)) & 1 ? odd : even;
vt.push_back(i);
}
vector<int> sequence;
for (int i = 1; i <= n; ++i) {
auto& ret = pref[i];
ret = pref[i - 1];
auto& vt = i & 1 ? odd : even;
if (!vt.size()) { ret = MAX; continue; }
sequence.push_back(vt.front());
ret += max(0ll, i - vt.front());
vt.pop_front();
}
if (pref[n] < MAX) {
answer = min(answer, pref[n]);
int total = 0;
for (int i = n - 1; i >= 1; i -= 2) {
swap(sequence[i - 1], sequence[i]);
total += max(0ll, i - sequence[i - 1]);
total += max(0ll, i + 1 - sequence[i]);
answer = min(answer, pref[i - 1] + total);
}
}
}
cout << (answer == MAX ? -1 : answer) << "\n";
}
