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#include <cstdio>
#include <cstring>

int a[500001], best[500001];



int main()
{
  int n;
  scanf("%d", &n);
  long long s = 0;
  for (int i = 1; i <= n; i++)
  {
    scanf("%d", a + i);
    s += a[i];
  }
  
  if (s < 0)
  {
    const int m1 = -1;
    printf("%d", m1);
    return 0;
  }
  
  memset(best, -1, sizeof(best));
  best[0] = 0;
  
  for (int i = 1; i <= n; i++)
  {
    long long sumf = 0, sume = 0;
    int mbest = 500001;
    if (a[i] == 0)
    {
      best[i] = best[i - 1];
    }
    else
    {
      for (int j = i; j >= 1; j--)
      {
        if (a[j] > 0) sume += a[j];
        if (a[j] < 0) sumf += a[j];
        
        if (sume >= -sumf && best[j - 1] >= 0 && i - j + best[j - 1] < mbest)
        {
          mbest = i - j + best[j - 1];
        }
      }
      if (mbest == 500001)
      {
        best[i] = -1;
      }
      else
      {
        best[i] = mbest;
      }
    }
    //printf("i = %d, best = %d\n", i, best[i]);
  }
  printf("%d", best[n]);
  
  return 0;
}