3
-1 1 -1
 4
45 -1 41 -1
 1
-1
 5
40 -1 44 46 48
 6
43 40 37 34 -1 -1
 7
-1 2 4 -1 4 1 5
 19
23 26 -1 -1 35 38 41 -1 -1 -1 53 -1 59 62 6 7 8 9 -1
 6
-1 2 6 -1 -1 6
 16
3 8 13 18 23 -1 -1 -1 43 48 53 45 -1 -1 -1 -1
 13
25 24 23 22 24 27 -1 33 -1 2 2 2 -1
 12
-1 17 -1 54 -1 64 -1 74 79 84 -1 94
 8
-1 12 14 16 18 20 -1 -1
 13
2 -1 3 1 3 1 -1 1 3 -1 -1 1 1
 5
-1 40 42 -1 46
 2
1000000000 -1
 14
-1 5 3 -1 -1 31 31 31 -1 31 -1 -1 4 7
 3
-1 1000000000 999999999
 7
32 33 34 -1 -1 37 38
 1
1000000000
 10
29 27 -1 23 42 -1 -1 45 -1 -1
 3
39 42 -1
 15
-1 28 -1 32 34 26 -1 26 -1 -1 26 26 26 -1 -1
 3
1000000000 999999999 1000000000
 17
-1 -1 -1 -1 64 68 72 -1 45 46 47 48 49 50 51 52 53
 3
-1 1 1000000000
 2
-1 1000000000
 3
999999999 -1 1000000000
 1
1
 2
1000000000 1000000000
 3
999999999 1000000000 -1
 7
11 8 5 -1 -1 -1 -1
 3
-1 1 2
 2
-1 21
 8
-1 -1 1 7 -1 9 5 2
 11
9 21 17 13 -1 -1 -1 -1 -1 -1 -1
 3
-1 1000000000 -1
 6
-1 6 1 -1 -1 -1
 1
65
 20
-1 32 37 -1 -1 -1 57 -1 -1 40 31 33 -1 -1 39 47 43 -1 35 32
 5
-1 1 7 -1 5
 18
21 19 -1 -1 -1 48 50 -1 54 -1 5 1 -1 -1 -1 37 36 35
 9
42 39 36 33 -1 -1 -1 34 39
 2
-1 -1

1
 1
 1
 1
 1
 3
 2
 2
 2
 3
 2
 1
 6
 1
 1
 3
 1
 1
 1
 2
 1
 2
 2
 2
 2
 1
 2
 1
 1
 1
 2
 2
 1
 3
 3
 1
 2
 1
 5
 2
 4
 2
 1

#include <bits/stdc++.h>
using namespace std;
struct Segment {
  vector<pair<long long, long long> > V;
  long long dif, sz, fp;
  Segment(long long fp) {
    dif = 0, sz = 0;
    this->fp = fp;
  }
  bool canAccept(long long num, long long pos) {
    if (V.size() == 0) return 1;
    if (V.size() == 1) {
      if (num == -1)
        return 1;
      else {
        long long dx = pos - V.back().second;
        long long dy = num - V.back().first;
        return dy % dx == 0;
      }
    } else {
      long long sz = V.size();
      long long dx = V[sz - 1].second - V[sz - 2].second;
      long long dy = V[sz - 1].first - V[sz - 2].first;
      long long actY = dy / dx * (pos - V[sz - 1].second) + V[sz - 1].first;
      long long firY = actY - (dy / dx) * (pos - fp);
      if (firY <= 0) return 0;
      return actY >= 1 && (num == -1 || actY == num);
    }
  }
  void add(long long num, long long pos) {
    if (num != -1) V.push_back(pair<long long, long long>(num, pos));
    sz++;
  }
};
int main() {
  int N;
  cin >> N;
  vector<int> V(N);
  for (int i = 0; i < N; ++i) cin >> V[i];
  Segment S(0);
  int cnt = 0;
  for (int i = 0; i < N; ++i) {
    if (S.canAccept(V[i], i))
      S.add(V[i], i);
    else {
      cnt++;
      S = Segment(i);
      S.add(V[i], i);
    }
  }
  if (S.sz) cnt++;
  cout << cnt << endl;
}
