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 ar[220000], start, ans;
vector<long long> has;
long long n, t, span, dv;
long long cur;
void nw() {
  has.clear();
  if (ar[cur] != -1) has.push_back(cur);
  start = cur;
  ans++;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  has.clear();
  start = 1;
  ans = 1;
  for (int i = 1; i <= n; i++) {
    cur = i;
    cin >> ar[i];
    if (ar[i] == -1) {
      if (has.size() < 2) continue;
      t = has.back();
      if (ar[t] + (i - t) * 1ll * span <= 0) nw();
      continue;
    }
    if (has.size() >= 2) {
      t = has.back();
      if ((ar[i] - ar[t]) != 1ll * span * (i - t)) {
        nw();
        continue;
      }
    }
    if (has.size() == 0) {
      has.push_back(i);
      continue;
    }
    t = has.back();
    span = i - t;
    dv = ar[i] - ar[t];
    if (dv % span) {
      nw();
      continue;
    };
    dv /= span;
    span = dv;
    t = ar[i] - 1ll * dv * (i - start);
    if (t <= 0) {
      nw();
      continue;
    }
    has.push_back(i);
  }
  cout << ans << endl;
  cin.get();
  cin.get();
  return 0;
}
