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 long long inf = 1LL << 60;
long long num[200020];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> num[i];
  int fni = 0, lni = 0, ind = 0;
  while (ind < n && num[ind] != -1) ind++;
  while (fni < n && num[fni] == -1) {
    fni++;
  }
  if (fni == n) {
    cout << 1 << endl;
    return 0;
  }
  lni = fni;
  int res = 1;
  int ci = fni, pi = fni;
  while (ci < n) {
    ci = fni, pi = fni;
    long long d = inf;
    while (ci < n) {
      ci++;
      if (ci < n && num[ci] != -1) {
        if ((num[ci] - num[pi]) % (ci - pi) != 0) {
          res++;
          break;
        } else {
          if (d == inf || (num[ci] - num[pi]) / (ci - pi) == d) {
            d = (num[ci] - num[pi]) / (ci - pi);
            pi = ci;
            lni = ci;
          } else {
            res++;
            break;
          }
        }
      }
    }
    if (d == inf) d = 0;
    int copy = fni - 1;
    while (copy >= ind && num[copy] == -1) {
      long long tmp = num[fni] - d * (fni - copy);
      if (tmp < 0)
        break;
      else
        num[copy] = tmp;
      copy--;
    }
    if (copy >= ind) {
      res++;
    }
    copy = lni + 1;
    while (copy < n && num[copy] == -1) {
      long long tmp = num[lni] + d * (copy - lni);
      if (tmp < 0) {
        ind = copy;
        break;
      } else
        num[copy] = tmp;
      copy++;
    }
    ind = copy;
    fni = ci;
    lni = fni;
  }
  cout << res << endl;
}
