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#include <iostream>
#include <set>

using namespace std;

const int N_MAX = 500 * 1000 + 5;

const int INF = 1000 * 1000 * 1000;
const int T = 1048576;
int tree[2 * T];

int querry(int a, int b) {
  a += T;
  b += T;
  int w = min(tree[a], tree[b]);

  while (a / 2 != b / 2) {
    if (a % 2 == 0)
      w = min(w, tree[a + 1]);
    if (b % 2 == 1)
      w = min(w, tree[b - 1]);

    a /= 2;
    b /= 2;
  }
  return w;
}

void update(int a, int x) {
  a += T;

  if (tree[a] <= x)
    return;

  tree[a] = x;

  while (a > 1) {
    a /= 2;
    tree[a] = min(tree[2 * a], tree[2 * a + 1]);
  }
}

int miasta[N_MAX + 1];
long long offset[N_MAX + 1];
long long index[N_MAX + 1];
int dp[N_MAX + 1];

set<long long> wartosci;
set<pair<long long, int>> indeksy;

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  int n;
  cin >> n;

  if (n == 0) {
    cout << "0\n";
    return 0;
  }

  if (n == 1) {
    int x;
    cin >> x;
    if (x >= 0)
      cout << "0\n";
    else
      cout << "-1\n";
    return 0;
  }

  for (int i = 0; i < n; i++) {
    cin >> miasta[i];
  }

  offset[0] = -miasta[0];
  index[0] = 0;
  dp[0] = INF;

  for (int i = 1; i < n; i++) {
    offset[i] = offset[i - 1] - miasta[i];
    index[i] = offset[i] + miasta[i];
    dp[i] = INF;
  }

  for (int i = 0; i < n; i++) {
    wartosci.insert(offset[i]);
    wartosci.insert(index[i]);
  }

  int nr = 0;
  for (auto &x : wartosci) {
    indeksy.insert(make_pair(x, nr++));
  }

  int maxIndex = nr - 1;

  for (int i = 0; i < n; i++) {
    offset[i] = indeksy.lower_bound(make_pair(offset[i], -1))->second;
    index[i] = indeksy.lower_bound(make_pair(index[i], -1))->second;
  }


  for (int i = T + maxIndex; i > 0; i--) {
    tree[i] = INF;
  }

  if (miasta[0] >= 0)
    dp[0] = 0;

  update((int)index[0], 0);

  for (int i = 1; i < n; i++) {
    if (dp[i - 1] < INF && miasta[i] >= 0)
      dp[i] = dp[i - 1];

    dp[i] = min(querry((int)offset[i], maxIndex) + i, dp[i]);

    update((int)index[i], dp[i - 1] - i);
  }

  if (dp[n - 1] < INF)
    cout << dp[n - 1] << "\n";
  else
    cout << -1 << "\n";
  return 0;
}