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#include <bits/stdc++.h>

#define ll long long
#define str string
#define pii pair<int, int>
#define pll pair<ll, ll>
#define fi first
#define se second

#define vc vector<char>
#define vvc vector<vc>
#define vi vector<int>
#define vll vector<ll>
#define vvi vector<vi>
#define vvll vector<vll>
#define vvvll vector<vvll>
#define vs vector<str>
#define vvs vector<vs>
#define vpii vector<pii>
#define vvpii vector<vpii>
#define vpll vector<pll>
#define vvpll vector<vpll>
#define vb vector<bool>
#define vvb vector<vb>
#define rep(i, a, b) for (int i = (a); i < int(b); i++)
#define repi(i, a, b) for (int i = (a); i <= int(b); i++)


using namespace std;
ll INF = LONG_LONG_MAX/2;
ll mod = 1000000000 + 7;

template <typename T, typename L>
void read(vector<T> & _data, L & _size, bool _shift) {
    _data.resize(_size + (ll)_shift);
    for (ll i = (ll)_shift; i < _size + (ll)_shift; i++)
        cin >> _data[i];
}

template <typename T, typename L>
void read(vector<vector<T>> & _data, L & _rows, L & _cols, bool _shiftRows, bool _shiftCols) {
    _data.resize(_rows + (ll)_shiftRows);
    for (ll i = 0; i < _rows + (ll)_shiftRows; i++)
        _data[i].resize(_cols + (ll)_shiftCols);
    for (ll i = (ll)_shiftRows; i < _rows + (ll)_shiftRows; i++)
        for (ll j = (ll)_shiftCols; j < _cols + (ll)_shiftCols; j++)
            cin >> _data[i][j];
}

template <typename T>
void write(vector<T> & _data, bool _shift) {
    for (ll i = (ll)_shift; i < _data.size(); i++)
        cout << _data[i] << " ";
    cout << endl;
}


//TODO: SOLUTION

vll tr;
ll m;
void mktr(ll n) {
    m = 1;
    while (m < n)
        m *= 2;
    tr = vll(2*m, INF); // min tree
}

void upd(ll x, ll val) {
    x += m;
    if (val >= tr[x])
        return;
    tr[x] = val;
    x /= 2;
    while (x > 0) {
        tr[x] = min(tr[2*x], tr[2*x + 1]);
        x /= 2;
    }
}

ll get(ll l, ll r) {
    l += m; r += m;
    ll mini = INF;

    while (l <= r) {
        if (l % 2 == 1) {
            mini = min(mini, tr[l]);
            l++;
        }
        if (r % 2 == 0) {
            mini = min(mini, tr[r]);
            r--;
        }
        l /= 2;
        r /= 2;
    }

    return mini;
}

void solve() {
    ll n; cin >> n;
    vll a; read(a, n, 1);
    vll suf(n + 2, 0);
    vll sortSuf;

    set<ll> ssuf;
    for (int i = n; i >= 1; i--) {
        suf[i] = suf[i + 1] + a[i];
        ssuf.insert(suf[i]);
    }
    ssuf.insert(suf[n + 1]);

    if (suf[1] < 0) {
        cout << -1 << endl;
        return;
    }

    for (long long x : ssuf) {
        sortSuf.push_back(x);
    }

    vll idInSorted(n + 2);
    for (int i = 1; i <= n + 1; i++) {
        idInSorted[i] = lower_bound(sortSuf.begin(), sortSuf.end(), suf[i]) - sortSuf.begin();
    }

    mktr(n);
    vll T(n + 1, INF);
    vll N(n + 1, INF);
    vll D(n + 1, INF);
    T[0] = N[0] = D[0] = 0;
    upd(idInSorted[1], 0);

    for (int i = 1; i <= n; i++) {
        if (a[i] < 0)
            N[i] = INF;
        else
            N[i] = D[i - 1];

        ll l = idInSorted[i + 1];
        ll r = sortSuf.size() - 1;
        T[i] = i + get(l, r) - 1;

        N[i] = min(N[i], INF);
        T[i] = min(T[i], INF);
        D[i] = min(N[i], T[i]);

        ll x = idInSorted[i + 1];
        upd(x, D[i] - i);
    }

    cout << D[n] << endl;
}


int main() {
    ios::sync_with_stdio(false);
    // TODO: Set value of this variable manually
    bool _multipleTestCases = false;

    if (_multipleTestCases) {
        ll t; cin >> t;
        while (t--)
            solve();
    }
    else {
        solve();
    }

    return 0;
}