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#include <cstdio>
#include <vector>
#include <algorithm>
#include <functional>

using namespace std;

typedef long long LL;

int main() {
  int n; scanf("%d", &n);
  vector<int> a; a.resize(n);
  for (int i=0; i<n; ++i) {
    scanf("%d", &a[i]);
  }

  vector<LL> sum; sum.resize(n+1);
  sum[0] = 0;
  for (int i=1; i<=n; ++i) {
    sum[i] = sum[i-1] + a[i-1];
  }

  if (sum[n] < 0) {
    printf("-1\n");
    return 0;
  }

  // Remembers energy taken per lines saved.
  vector<LL> optimal;
  optimal.push_back(0);

  for (int i=0; i<n; ++i) {
    LL energy = sum[i+1];
    if (energy < 0) continue;
    if (energy > sum[n]) continue;
    auto it = upper_bound(optimal.begin(), optimal.end(), energy);
    
 //   printf("Can remove %d at %d and save %d\n", energy, i, it-optimal.begin());

    if (it == optimal.end()) {
      optimal.push_back(sum[i+1]);
    } else {
      *it = energy;
    }
  }

  printf("%lld\n", n + 1 - static_cast<LL>(optimal.size()));
  return 0;
}