#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
template <typename T> inline void read(T &F) {
    int R = 1; F = 0; char CH = getchar();
    for(; !isdigit(CH); CH = getchar()) if(CH == '-') R = -1;
    for(; isdigit(CH); CH = getchar()) F = F * 10 + CH - 48;
    F *= R;
}
inline void file(string str) {
    freopen((str + ".in").c_str(), "r", stdin);
    freopen((str + ".out").c_str(), "w", stdout);
}
const int N = 5e5 + 10;
int n, ai[N]; map<int, vector<int> > M;
LL f[N], g[N]; int tot;
int calc(int x, int y) {
    return abs(x - y);
}
vector<LL> calc(int x, int l, int r) {
    //cerr << x << ' ' << l << ' ' << r << endl;
    const int u = M[x].size(), v = M[-x].size(), m = u + v;
    vector<LL> b(m + 1);
    for(auto &i : b) i = 1e18;
    if((m + (r & 1)) / 2 == v) {
        vector<int> c[2] = {M[x], M[-x]};
        b[0] = 0; int L = l, R = r - m + 1;
        for(int i = r - m + 1; i <= r; i++)
            b[0] += calc(c[i & 1].back(), i), c[i & 1].pop_back();
        c[0] = M[x], c[1] = M[-x]; 
        for(int i = 2; i <= m; i += 2) {
            b[i] = b[i - 2];
            b[i] -= calc(c[R & 1].back(), R); R++;
            b[i] -= calc(c[R & 1].back(), R); R++;
            b[i] += calc(c[(L ^ 1) & 1].back(), L); L++;
            b[i] += calc(c[(L ^ 1) & 1].back(), L); L++;
            c[0].pop_back(), c[1].pop_back();
        }
    }
    if(m >= 1 && (m - 1 + (r & 1)) / 2 + ((l ^ 1) & 1) == v) {
        vector<int> c[2] = {M[x], M[-x]};
        int L = l + 1, R = r - m + 2;
        b[1] = calc(c[(l ^ 1) & 1].back(), l); c[(l ^ 1) & 1].pop_back();
        for(int i = r - m + 2; i <= r; i++)
            b[1] += calc(c[i & 1].back(), i), c[i & 1].pop_back();
        c[0] = M[x], c[1] = M[-x]; c[(l ^ 1) & 1].pop_back();
        for(int i = 3; i <= m; i += 2) {
            b[i] = b[i - 2];
            b[i] -= calc(c[R & 1].back(), R); R++;
            b[i] -= calc(c[R & 1].back(), R); R++;
            b[i] += calc(c[(L ^ 1) & 1].back(), L); L++;
            b[i] += calc(c[(L ^ 1) & 1].back(), L); L++;
            c[0].pop_back(), c[1].pop_back();
        }
    }
    return b;
}
int main() {
    //file("test");
    read(n); vector<int> R;
    for(int i = 1; i <= n; i++) {
        read(ai[i]);
        if(i & 1) ai[i] = -ai[i];
        M[ai[i]].emplace_back(i);
        R.emplace_back(abs(ai[i]));
    }
    sort(R.begin(), R.end());
    R.erase(unique(R.begin(), R.end()), R.end());
    reverse(R.begin(), R.end());
    for(auto &i : M) sort(i.second.begin(), i.second.end(), greater<int>());
    for(int i = 1; i <= n; i++) f[i] = 1e18;
    for(int i : R) {
        if(i == 0) continue;
        for(int j = tot; j >= 0; j--) {
            auto c = calc(i, j + 1, n - (tot - j));
            for(int k = 1; k < c.size(); k++)
                f[j + k] = min(f[j + k], f[j] + c[k]);
            f[j] = min((LL)(1e18), f[j] + c[0]);
        }
        tot += M[i].size() + M[-i].size();
    }
    auto tmp = M[0]; sort(tmp.begin(), tmp.end());
    for(int i = 0; i < tmp.size(); i++) {
        int x = tmp[i] - i - 1;
        g[x + 1] += 2; g[1]--; g[0] += x, g[1] -= x;
    }
    for(int i = 1; i <= tot; i++) g[i] += g[i - 1];
    for(int i = 1; i <= tot; i++) g[i] += g[i - 1];
    LL ans = 1e18;
    for(int i = 0; i <= tot; i++) ans = min(ans, f[i] + g[i]);
    if(ans == (LL)(1e18)) puts("-1");
    else cout << ans / 2 << '\n';
    
    #ifdef _MagicDuck
        fprintf(stderr, "# Time: %.3lf s", (double)clock() / CLOCKS_PER_SEC);
    #endif
    return 0;
}