#include<bits/stdc++.h>
#define L(i, j, k) for(int i = (j); i <= (k); ++i)
#define R(i, j, k) for(int i = (j); i >= (k); --i)
#define ll long long
#define sz(a) ((int) (a).size())
#define vi vector < int >
#define me(a, x) memset(a, x, sizeof(a))
#define ull unsigned long long
#define ld __float128
#define pb emplace_back
using namespace std;
#define i128 __int128
const int N = 1e6 + 7;
template < int N > struct fenwt {
	using F = long long ;
	F a[N + 1];
	void add (int x, F w) {
		for (; x <= N; x += x & -x) a[x] += w;
	}
	F query (int x) {
		F ret = 0;
		for (; x; x -= x & -x) ret += a[x];
		return ret;
	}
	F get (int l, int r) {
		if(l > r) return 0;
		return query (r) - query (l - 1);
	}
} ;
fenwt < N > F, G;
int n;
int h[N];
int arr[N], tot;
vector<pair<int,int>>seg[N];
ll dp[2][2];
ll ndp[2][2];
/* 0 : negative ; 1 : positive */
struct node{
	ll v1, v2;
	ll i1, i2;
	node() {
		v1 = v2 = i1 = i2 = -1;
	}	
};
map<int,node>qwq[N];
int main() {
	ios :: sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	cin >> n;
	L(i, 1, n) {
		cin >> h[i];
		if(i % 2 == 0) {
			h[i] = -h[i];
		}
	}
	L(i, 1, n)
		if(h[i])
			arr[++tot] = abs(h[i]);
	sort(arr + 1, arr + tot + 1);
	tot = unique(arr + 1, arr + tot + 1) - arr - 1;
	L(i, 1, n)
		if(h[i]) {
			int ab = abs(h[i]);
			ab = lower_bound(arr + 1, arr + tot + 1, ab) - arr;
			if(h[i] > 0) seg[ab].pb(i, 1);
			else seg[ab].pb(i, 0);
		}
	L(i, 1, n) {
		F.add(i, 1);
	}
	me(dp, 0x3f);
	dp[0][n & 1] = 0;
	R(i, tot, 1) {
		// cout << i << " : ";
		vi ps[2];
		for(auto&u : seg[i]) 
			ps[u.second].pb(u.first);
			// cout << "(" << u.first << ',' << u.second << "), ";
		// cout << endl;
		me(ndp, 0x3f);
		L(x, 0, 1) L(y, 0, 1) if(dp[x][y] < 1e17) {
			int cp = x;
			int pt[2] = {0, 0};
			ll w = 0;
			while(true) {
				auto &D = qwq[pt[0]][pt[1]];
				D.v1 = w, D.i1 = cp;
				// cout << pt[0] << ' ' << pt[1] << " : " << w << endl;
				if(pt[cp] >= sz(ps[cp])) 
					break;
				w += F.query(ps[cp][pt[cp]] - 1);
				F.add(ps[cp][pt[cp]], -1);
				++pt[cp];
				cp ^= 1;
			}
			L(o, 0, 1) L(j, pt[o], sz(ps[o]) - 1)F.add(ps[o][j], -1);
			pt[0] = sz(ps[0]), pt[1] = sz(ps[1]);
			cp = y, w = 0;
			while(true) {
				auto &D = qwq[pt[0]][pt[1]];
				D.v2 = w, D.i2 = cp;
				// cout << pt[0] << ' ' << pt[1] << " : " << w << endl;
				if(pt[cp] <= 0)break;
				--pt[cp];
				w += F.query(n) - F.query(ps[cp][pt[cp]]);
				w += G.query(ps[cp][pt[cp]]);
				G.add(ps[cp][pt[cp]], 1);
				cp ^= 1;
			}
			L(o, 0, 1) L(j, 0, sz(ps[o]) - 1)F.add(ps[o][j], 1);
			L(o, 0, 1) L(j, pt[o], sz(ps[o]) - 1)G.add(ps[o][j], -1);
			L(i, 0, sz(ps[0])) {
				for(auto&t : qwq[i]) {
					auto V = t.second;
					if(V.i1 >= 0 && V.i2 >= 0)
						ndp[V.i1][V.i2] = min(ndp[V.i1][V.i2], dp[x][y] + V.v1 + V.v2);
				}
				qwq[i].clear();
			}
		}
		swap(dp, ndp);
		for(auto&u : seg[i])
			F.add(u.first, -1);
		// L(i, 0, 1) {
		// 	L(j, 0, 1) {
		// 		cout << dp[i][j] << " ";
		// 	}
		// 	cout << endl;
		// }
		// cout << endl;
	}
	ll ans = 1e18;
	L(i, 0, 1)L(j, 0, 1)ans = min(ans, dp[i][j]);
	if(ans > 1e17)cout << -1 << '\n';
	else cout << ans << '\n';
	return 0;
}