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#include <bits/stdc++.h>
#include <math.h>
using namespace std;
#define endl "\n"
#define mp make_pair
#define st first
#define nd second
#define pii pair<int, int>
#define pb push_back
#define _upgrade ios_base::sync_with_stdio(0), cout.setf(ios::fixed), cout.precision(10), cin.tie(0), cout.tie(0);
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define FWD(i, a, b) for (int i = (a); i < (b); ++i)
#define rep(i, n) for (int32_t i = 0; i < (n); ++i)
#define fwd(i, a, b) for (int i = (a); i < (b); ++i)
#define all(c) (c).begin(), (c).end()
#define sz(X) (int)((X).size())
#define what(x) cerr << #x << " is " << x << endl;

ostream &operator<<(ostream &out, string str) {
   for (char c : str)
      out << c;
   return out;
}
template <class L, class R> ostream &operator<<(ostream &out, pair<L, R> p) { return out << "(" << p.st << ", " << p.nd << ")"; }
template <class T> auto operator<<(ostream &out, T a) -> decltype(a.begin(), out) {
   out << '{';
   for (auto it = a.begin(); it != a.end(); it = next(it))
      out << (it != a.begin() ? ", " : "") << *it;
   return out << '}';
}
void dump() { cerr << "\n"; }
template <class T, class... Ts> void dump(T a, Ts... x) {
   cerr << a << ", ";
   dump(x...);
}
#define DEBUG false
#define debug(...)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     \
   if (DEBUG)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          \
   cerr << "[" #__VA_ARGS__ "]: ", dump(__VA_ARGS__)
#define int long long

const int inf = (int)1e18;
int n;
vector<int> dp;
vector<int> sum;
map<int, int> M;

pii get(int key) { return *(--M.upper_bound(key)); }

void insert(int key, int val) {

   auto lepszy = get(key);
   if (lepszy.nd <= val) {
      // exit(-1);
      return;
   }

   M[key] = val;

   auto ptr = M.upper_bound(key);
   while (ptr != M.end()) {
      if (ptr->nd < val)
         return;
      // debug("USUWAM: ", *ptr);
      ptr = M.erase(ptr);
   }
}

void pre() {
   M[-inf] = inf;
   insert(0, 0);

   cin >> n;
   sum.resize(n + 1, 0);
   dp.resize(n + 1, 0);

   rep(i, n) {
      cin >> sum[i + 1];
      sum[i + 1] += sum[i];
   }
}
void solve() {
   for (int i = 1; i <= n; i++) {
      auto r = get(sum[i]);
      // debug(i, M, r);
      dp[i] = r.nd + i - 1;
      insert(sum[i], dp[i] - i);
   }
   // debug(dp);
}

int32_t main() {
   _upgrade;
   pre();
   solve();
   if (dp[n] >= 2 * n)
      cout << -1 << endl;
   else
      cout << dp[n] << endl;
}