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;
long long a[300041];
int main() {
  long long n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i];
  long long s = 0, ii = 0, i = -1, j = -1, step = 2e10 + 4141, ans = 0, f;
  while (s < n) {
    if (i == -1) {
      while (a[s] == -1 && s < n) s++;
      if (s == n) {
        ans++;
        break;
      }
      i = s;
      f = 1;
      s++;
      if (s == n) {
        ans++;
        break;
      }
    }
    int ff = 0;
    while (a[s] == -1 && s < n) {
      if (step != -1 && a[i] + step * (s - i + ii) <= 0) {
        ii = s;
        i = -1;
        step = 2e10 + 4141;
        ans++;
        ff = 1;
        break;
      }
      s++;
    }
    if (ff) continue;
    if (s == n) {
      ans++;
      break;
    }
    j = s;
    if (j - i == 1) {
      if (step == 2e10 + 4141) {
        step = a[j] - a[i];
        if (f && a[i] - step * (i - ii) <= 0) {
          ans++;
          i = j;
          s++;
          if (s == n) ans++;
          f = 0;
          step = 2e10 + 4141;
          continue;
        }
        s++;
        f = 0;
        if (s == n) ans++;
      } else if (a[j] - a[i] != step) {
        ans++;
        s++;
        i = j;
        f = 0;
        step = 2e10 + 4141;
        if (s == n) ans++;
      }
      continue;
    }
    if (((a[j] - a[i]) / (j - i)) * (j - i) != a[j] - a[i] ||
        (((a[j] - a[i]) / (j - i)) * (j - i) == a[j] - a[i] &&
         step != (a[j] - a[i]) / (j - i) && step != 2e10 + 4141)) {
      ans++;
      i = j;
      f = 0;
      s++;
      step = 2e10 + 4141;
      if (s == n) ans++;
      continue;
    }
    step = (a[j] - a[i]) / (j - i);
    if (f && a[i] - step * (i - ii) <= 0) {
      ans++;
      i = j;
      s++;
      if (s == n) ans++;
      f = 0;
      step = 2e10 + 4141;
      continue;
    }
    f = 0;
    s++;
    if (s == n) ans++;
  }
  cout << ans;
  return 0;
}
