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;
int main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  int a[n];
  bool b = true;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] != -1) b = false;
  }
  if (b)
    cout << "1" << endl;
  else {
    int last = 0;
    int count = 0;
    for (int i = 0; i < n; i++) {
      int first = -1;
      for (int j = i; j < n; j++)
        if (a[j] != -1) {
          first = j;
          break;
        }
      b = true;
      int second = -1;
      for (int j = first + 1; j < n; j++)
        if (a[j] != -1) {
          second = j;
          break;
        }
      if (second == -1) {
        count++;
        break;
      }
      count++;
      i++;
      int d = (a[first] - a[second]) / (second - first);
      if (d * (second - first) != a[first] - a[second]) continue;
      if (a[first] + d * (first - last) <= 0) continue;
      last = second;
      i = last;
      bool _Break = false;
      while (true) {
        if (last + 1 >= n) break;
        bool _break = false, tmp = true;
        for (int j = last + 1; j < n; j++)
          if (a[j] != -1) {
            tmp = false;
            if (a[last] - a[j] != d * (j - last)) {
              _break = true;
              last = j;
              i = j - 1;
            } else {
              last = j;
              i = last;
            }
            break;
          }
        if (tmp) _Break = true;
        if (_break || tmp) break;
      }
      if (_Break) break;
    }
    cout << count << endl;
  }
  return 0;
}
