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;
const int MAX_N = 200100;
int a[MAX_N];
int pre[MAX_N];
int post[MAX_N];
int before(int val, int step) {
  if (step > 0) return (val - 1) / step;
  return 100000000;
}
int after(int val, int step) {
  if (step < 0) return -(val - 1) / step;
  return 100000000;
}
int main() {
  int n;
  cin >> n;
  int m = 0;
  int gaps = 0;
  for (int i = 0; i < n; ++i) {
    int t;
    cin >> t;
    if (t == -1)
      ++gaps;
    else {
      if (m > 0) {
        post[m - 1] = gaps;
      }
      pre[m] = gaps;
      a[m] = t;
      gaps = 0;
      ++m;
    }
  }
  if (m > 0) post[m - 1] = gaps;
  if (m <= 1) {
    cout << "1";
    return 0;
  }
  int ans = 0;
  int c = 0;
  bool ended = true;
  for (int i = 0; i < m; ++i) {
    if (i + 1 >= m) {
      ++ans;
      if (!ended && after(a[i], c) < post[i]) ++ans;
      continue;
    }
    int b = post[i] + 1;
    int d = a[i + 1] - a[i];
    if (ended) {
      if (d % b == 0) {
        c = d / b;
        if (before(a[i], c) < pre[i]) {
          ++ans;
          pre[i + 1] = 0;
        } else {
          ended = false;
        }
      } else {
        ++ans;
        pre[i + 1] = 0;
      }
    } else {
      if (a[i + 1] != a[i] + b * c) {
        int aft = min(after(a[i], c), pre[i + 1]);
        pre[i + 1] -= aft;
        ++ans;
        ended = true;
      }
    }
  }
  cout << ans << endl;
  return 0;
}
