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 inf = (int)1e9;
const double INF = 1e12, EPS = 1e-9;
int n, a[200000];
int main() {
  cin >> n;
  for (int i = 0; i < (int)n; i++) cin >> a[i];
  int ans = 1;
  for (int i = 0; i < (int)n; i++) {
    int j, k;
    for (j = i + 1; j < n && a[j] < 0; j++)
      ;
    for (k = j + 1; k < n && a[k] < 0; k++)
      ;
    if (j >= n) break;
    if (a[i] < 0) {
      if (k >= n) break;
      if ((a[k] - a[j]) % (k - j)) {
        ans++;
        i = k - 1;
        continue;
      }
      int d = (a[k] - a[j]) / (k - j);
      if (a[j] - (long long)d * (j - i) <= 0) {
        ans++;
        i = k - 1;
        continue;
      }
      i = j - 1;
      continue;
    }
    if (k >= n) {
      if ((a[j] - a[i]) % (j - i)) {
        ans++;
        break;
      }
      int d = (a[j] - a[i]) / (j - i);
      if (a[j] + (long long)d * (n - 1 - j) <= 0) ans++;
      break;
    }
    if ((a[j] - a[i]) % (j - i)) {
      i = j - 1;
      ans++;
      continue;
    }
    int d = (a[j] - a[i]) / (j - i);
    int d2 = (a[k] - a[j]) % (k - j) ? 2 * inf + 1 : (a[k] - a[j]) / (k - j);
    for (j = i + 1; j < k; j++) {
      a[j] = a[j - 1] + d;
      if (a[j] <= 0) break;
    }
    if (j < k) {
      a[j] = -1;
      i = j - 1;
      ans++;
      continue;
    }
    if (d != d2) {
      ans++;
      i = k - 1;
    } else
      i = k - 2;
  }
  cout << ans << endl;
  return 0;
}
