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#include <bits/stdc++.h>

using namespace std;

#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return {i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (c it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(x...) " [" #x ": " << (x) << "] "

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
template <typename A, typename B>
using unordered_map2 = __gnu_pbds::gp_hash_table<A, B>;
using namespace __gnu_pbds;
template <typename T> using ordered_set =
  __gnu_pbds::tree<T, __gnu_pbds::null_type, less<T>, __gnu_pbds::rb_tree_tag,
                   __gnu_pbds::tree_order_statistics_node_update>;
// ordered_set<int> s; s.insert(1); s.insert(2);
// s.order_of_key(1);    // Out: 0.
// *s.find_by_order(1);  // Out: 2.

using ld = long double;
using ll = long long;

constexpr int mod = 1000 * 1000 * 1000 + 7;
constexpr int odw2 = (mod + 1) / 2;

void OdejmijOd(int& a, int b) { a -= b; if (a < 0) a += mod; }
int Odejmij(int a, int b) { OdejmijOd(a, b); return a; }
void DodajDo(int& a, int b) { a += b; if (a >= mod) a -= mod; }
int Dodaj(int a, int b) { DodajDo(a, b); return a; }
int Mnoz(int a, int b) { return (ll) a * b % mod; }
void MnozDo(int& a, int b) { a = Mnoz(a, b); }
int Pot(int a, ll b) { int res = 1; while (b) { if (b % 2 == 1) MnozDo(res, a); a = Mnoz(a, a); b /= 2; } return res; }
int Odw(int a) { return Pot(a, mod - 2); }
void PodzielDo(int& a, int b) { MnozDo(a, Odw(b)); }
int Podziel(int a, int b) { return Mnoz(a, Odw(b)); }
int Moduluj(ll x) { x %= mod; if (x < 0) x += mod; return x; }

template <typename T> T Maxi(T& a, T b) { return a = max(a, b); }
template <typename T> T Mini(T& a, T b) { return a = min(a, b); }

struct Potega {
  vector<int> tab;

  void Init(int n) {
    tab.resize(n, numeric_limits<int>::max());
  }

  void Set(int i, int val) {
    i++;
    while (i <= (int) tab.size()) {
      Mini(tab[i - 1], val);
      i += (i & -i);
    }
  }

  int Read(int i) {
    int result = numeric_limits<int>::max();
    i++;
    while (i > 0) {
      Mini(result, tab[i - 1]);
      i -= (i & -i);
    }
    return result;
  }
};

struct Przyp {

int n;
vector<ll> pref;
vector<pair<ll, int>> kolejka;

Potega pot;

int Run() {
  cin >> n;
  pref.resize(n + 1);
  for (int i = 1; i <= n; i++) {
    cin >> pref[i];
    pref[i] += pref[i - 1];
    if (pref[i] >= 0) {
      kolejka.emplace_back(pref[i], i);
    }
  }
  sort(kolejka.begin(), kolejka.end());
  pot.Init(n + 1);
  pot.Set(0, 0);

  for (const auto& [ignore, i] : kolejka) {
    const int val = pot.Read(i);
    debug() << imie(ignore) imie(i) imie(val);
    if (i == n) {
      if (val == numeric_limits<int>::max()) {
        return -1;
      }
      return val + i - 1;
    }
    if (val != numeric_limits<int>::max()) {
      debug() << imie(ignore) imie(i) imie(val) imie(val + i - 1);
      pot.Set(i, val - 1);
    }
  }
  return -1;
}

};  // struct Przyp

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  cout << Przyp().Run() << endl;
  return 0;
}