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 N = 2e5 + 5;
long long n;
long long a[N];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  while (cin >> n) {
    for (int i = 1; i <= n; i++) cin >> a[i];
    a[n + 1] = -2;
    bool star = 1, ok = 0;
    long long cnt = 0, d = 0, ans = 0;
    for (int i = 1; i <= n; i++) {
      if (a[i] == -1 && !ok && star)
        cnt++;
      else if (a[i] == -1 && ok) {
        if (a[i - 1] + d > 0)
          a[i] = a[i - 1] + d;
        else
          ans++, cnt = 1, star = 1, ok = 0;
      } else if (a[i] == -1 && !star) {
        int j = i + 1;
        while (a[j] == -1) j++;
        if (a[j] == -2) break;
        long long dis = j + 1 - i;
        long long diff = a[j] - a[i - 1];
        if (diff % dis == 0) {
          ok = 1;
          d = diff / dis;
          i = j;
        } else
          ok = 0, star = 1, i = j - 1, ans++;
      } else if (a[i] != -1 && cnt) {
        int j = i + 1;
        while (a[j] == -1) j++;
        if (a[j] == -2) break;
        long long dis = j - i;
        long long diff = a[j] - a[i];
        if (diff % dis == 0) {
          d = diff / dis;
          if (a[i] - d * cnt > 0)
            ok = 1, star = 0, i = j;
          else
            i = j - 1, ok = 0, star = 1, ans++;
        } else
          i = j - 1, ok = 0, star = 1, ans++;
        cnt = 0;
      } else if (star)
        star = 0;
      else if (!ok)
        d = a[i] - a[i - 1], ok = 1;
      else if (a[i - 1] + d != a[i])
        ans++, star = 1, ok = 0, i--;
    }
    cout << ans + 1 << endl;
  }
  return 0;
}
