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#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>

using namespace std;

typedef long long ll;
int BLOK;
const int INF = 1000000000;

struct ele
{
    ll suf;
    int b, nr;
};

bool por(ele a, ele b)
{
    if (a.suf < b.suf)
        return true;
    if (a.suf > b.suf)
        return false;
    return a.nr < b.nr;
}

ll Pref(vector<ll>& a, int l, int r)
{
    ll s = a[r];
    if (l != 0)
        s -= a[l - 1];
    return s;
}

int Szukaj(vector<ele>& a, ll x)
{
    int l = 0, p = a.size() - 1, s, r = -1;
    while (l <= p)
    {
        s = (l + p) >> 1;
        if (a[s].suf >= x)
        {
            r = s;
            p = s - 1;
        }
        else
            l = s + 1;
    }
    return r;
}

int main()
{
    ios_base::sync_with_stdio(0);
    int n;
    cin >> n;
    BLOK = 1000;
    vector<ll> pref(n);
    for (int i = 0; i < n; ++i)
    {
        cin >> pref[i];
        if (i != 0)
            pref[i] += pref[i - 1];
    }
    if (pref[n - 1] < 0)
    {
        cout << "-1";
        return 0;
    }
    vector<int> l, p;
    for (int i = 0; i < n; i += BLOK)
    {
        l.push_back(i);
        p.push_back(min(i + BLOK - 1, n - 1));
    }
    int ilBlokow = l.size();
    vector<int> dp(n, INF);
    vector<ll> sumBloku(ilBlokow, 0);
    vector< vector<ele> > wart(ilBlokow);
    for (int i = 0; i < ilBlokow; ++i)
    {
        int L = l[i], P = p[i];
        for (int j = L; j <= P; ++j)
        {
            if (j != 0 && pref[j] == pref[j - 1])
            {
                dp[j] = dp[j - 1];
                continue;
            }
            for (int k = L; k <= j; ++k)
            {
                if (k != 0)
                {
                    if (Pref(pref, k, j) >= 0 && dp[k - 1] != INF)
                        dp[j] = min(dp[j], dp[k - 1] + j - k);
                }
                else
                {
                    if (Pref(pref, k, j) >= 0)
                        dp[j] = min(dp[j], j);
                }
            }
            for (int k = 0; k < i; ++k)
            {
                sumBloku[k] += Pref(pref, j, j);
                int gdzie = Szukaj(wart[k], -sumBloku[k]);
                if (gdzie != -1)
                    dp[j] = min(dp[j], j + wart[k][gdzie].b);
            }
        }
        for (int j = L; j <= P; ++j)
        {
            if (j == 0)
                wart[i].push_back({Pref(pref, j, P), 0, j});
            else
            {
                if (dp[j - 1] != INF)
                    wart[i].push_back({Pref(pref, j, P), dp[j - 1] - j, j});
            }
        }
        sort(wart[i].begin(), wart[i].end(), por);
        for (int j = (int) wart[i].size() - 2; j >= 0; --j)
            wart[i][j].b = min(wart[i][j].b, wart[i][j + 1].b);
    }
    cout << dp[n - 1];
    return 0;
}