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#include <bits/stdc++.h>

#define FOR(i, b, e) for (int i = (b); i <= (e); i++)
#define FORD(i, b, e) for (int i = (e); i >= (b); i--)
#define MP make_pair
#define FS first
#define ND second
#define PB push_back
#define ALL(x) x.begin(), x.end()

using namespace std;

using LL = long long;
using PII = pair<int,int>;
using PLL = pair<LL,LL>;
using VI = vector<int>;
using VLL = vector<LL>;
template<class T>
using V = vector<T>;

template<class T>
int sz(const T& a) { return (int)a.size(); }
template<class T>
void amin(T& a, T b) { a = min(a, b); }
template<class T>
void amax(T& a, T b) { a = max(a, b); }

const int inf = 1e9;
const LL infl = 1e18;

const int N = int(5e5) + 1;

mt19937 rnd;
int p[N], l[N], r[N];
int mn[N], val[N], f;
LL key[N];

void update(int i)
{
  mn[i] = val[i];
  amin(mn[i], mn[l[i]]);
  amin(mn[i], mn[r[i]]);
}

int join(int i, int j)
{
  if (!i) return j;
  if (!j) return i;
  if (p[i] < p[j]) {
    r[i] = join(r[i], j);
    update(i);
    return i;
  }
  l[j] = join(i, l[j]);
  update(j);
  return j;
}

// [< v, >= v]
PII split(int k, LL x)
{
  if (!k) return MP(0, 0);
  PII s;
  if (key[k] < x) {
    s = split(exchange(r[k], 0), x);
    update(k);
    return MP(join(k, s.FS), s.ND);
  }
  s = split(exchange(l[k], 0), x);
  update(k);
  return MP(s.FS, join(s.ND, k));
}

int find(int k, LL x)
{
  if (!k || key[k] == x) return k;
  return find(x < key[k] ? l[k] : r[k], x);
}

int singleton(LL x, int y)
{
  f++;
  key[f] = x;
  val[f] = y;
  update(f);
  return f;
}

int n, t, ans = inf, a[N], b[N], dp[N];
LL s[N];

int get_min(LL x)
{
  int res = inf;
  auto [t1, t2] = split(t, x + 1);
  if (t1) res = mn[t1];
  t = join(t1, t2);
  return res;
}

int main()
{
  scanf("%d", &n);

  uint32_t h = 2137;
  FOR(i, 1, n) {
    scanf("%d", &a[i]);
    h = (31u * h + a[i]);
    s[i] += s[i - 1] + a[i];
  }

  rnd.seed(h);
  iota(p, p + N, 0);
  shuffle(p, p + N, rnd);
  mn[0] = inf;
  val[0] = inf;


  if (s[n] < 0) {
    puts("-1");
    exit(0);
  }

  int k = inf;
  FORD(i, 1, n) {
    b[i] = k;
    if (a[i]) k = i;
  }

  if (k == inf) {
    puts("0");
    exit(0);
  }

  t = singleton(0, -k);
  FOR(i, 1, n) if (a[i]) {
    dp[i] = get_min(s[i]);
    if (dp[i] == inf) continue;
    dp[i] += i;
    if (b[i] != inf) {
      int y = min(val[find(t, s[i])], dp[i] - b[i]);
      auto [t1, t2] = split(t, s[i]);
      t = join(t1, join(singleton(s[i], y), split(t2, s[i] + 1).ND));
    }
  }

  FORD(i, 1, n) if (a[i]) {
    amin(ans, dp[i]);
    if (a[i] < 0) break;
  }

  printf("%d\n", ans);
}