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#include <bits/stdc++.h>
using namespace std;
#define PII pair<int, int>
#define VI vector<int>
#define VPII vector<PII>
#define LL long long
#define LD long double
#define f first
#define s second
#define MP make_pair
#define PB push_back
#define endl '\n'      // UWAGA
#define ALL(c) (c).begin(), (c).end()
#define SIZ(c) (int)(c).size()
#define REP(i, n) for(int i = 0; i < (int)(n); ++i)
#define FOR(i, b, e) for(int i = (b); i <= (int)(e); ++i)
#define FORD(i, b, e) for(int i = (b); i >= (int)(e); --i)
#define random_shuffle(V) shuffle(V, rng)

#define sim template<class n
sim, class s> ostream & operator << (ostream &p, pair<n, s> x)
{return p << "<" << x.f << ", " << x.s << ">";}
sim> auto operator << (ostream &p, n y) ->
typename enable_if<!is_same<n, string>::value, decltype(y.begin(), p)>::type 
{int o = 0; p << "{"; for(auto c: y) {if(o++) p << ", "; p << c;} return p << "}";}
void dor() {cerr << endl;}
sim, class...s> void dor(n p, s...y) {cerr << p << " "; dor(y...);}
sim, class s> void mini(n &p, s y) {if(p>y) p = y;}
sim, class s> void maxi(n &p, s y) {if(p<y) p = y;}
#ifdef DEB
#define debug(...) dor(__FUNCTION__, ":", __LINE__, ": ", __VA_ARGS__)
#else
#define debug(...)
#endif 

#define I(x) #x " =", (x), " "
#define A(a, i) #a "[" #i " =", i, "] =", a[i], " "

const int BASE = 1 << 19;
int tree[BASE * 2];
void insert(int a, int val)
  {
  a += BASE + 1;
  while(a)
    {
    mini(tree[a], val);
    a /= 2;
    }
  }
int query(int a, int b)
  {
  a += BASE;
  b += BASE + 2;
  int res = 1e9;
  while(a / 2 != b / 2)
    {
    if(a % 2 == 0)mini(res, tree[a+1]);
    if(b % 2 == 1)mini(res, tree[b-1]);
    a /= 2;
    b /= 2;
    }
  return res;
  }

const int MXN = 1000 * 500 + 15;
int in[MXN];
LL suf[MXN];
int ord[MXN]; // rosnąco sufiksy posortowane, w razie remisu późniejszy wcześniej
int where[MXN]; // gdzie co jest w ord

int main()
  {
  int n;
  scanf("%d", &n);
  FOR(i, 1, n)
    {
    scanf("%d", &in[i]);
    }
  FORD(i, n, 0)
    {
    suf[i] = suf[i+1] + in[i];
    ord[i] = i;
    }
  if(suf[1] < 0)
    {
    puts("-1");
    return 0;
    }
  sort(ord, ord + n + 1, [&](int a, int b){return suf[a+1] < suf[b+1] || (suf[a+1] == suf[b+1] && a > b);});
  FOR(i, 0, n)
    where[ord[i]] = i;

  REP(i, BASE*2)tree[i] = 1e8;
  insert(where[0], 0); // poza zerem

  FOR(i, 1, n)
    {
    int best = query(where[i], n); // jeśli kończe przedział tutaj
    insert(where[i], best-1);      // zmniejszam best o 1, to samo co dodanie 1 do reszty
    }
  printf("%d\n", query(where[n], where[n]) + n);
  }