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;
vector<pair<int, int> > als;
queue<int> uls;
int a[200000];
int q[200000];
int n, p = -1, res, dif = 1000000000;
void check(int i) {
  while (!uls.empty()) {
    a[uls.front()] = a[i] - (i - uls.front()) * dif;
    if (a[uls.front()] <= 0) {
      res++;
      while (!uls.empty()) uls.pop();
    } else
      uls.pop();
  }
  return;
}
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] != -1) als.push_back(pair<int, int>(a[i], i));
  }
  if (n == 1) {
    cout << 1;
    return 0;
  }
  for (int i = 0; i < n; i++) {
    if (a[i] == -1) {
      if (i == n - 1) q[i] = ++res;
      if (dif != 1000000000 && a[i - 1] - dif >= 0) {
        a[i] = a[i - 1] - dif, q[i] = q[i - 1];
      }
      uls.push(i);
      continue;
    }
    p++;
    if (p == 0) continue;
    if (a[i - 1] != -1 && a[i] - a[i - 1] != dif) {
      if (i < n - 1) {
        res++;
        dif = (als[p + 1].first - als[p].first) /
              (als[p + 1].second - als[p].second);
      } else {
        q[i] = ++res;
        q[i - 1] = res;
        dif = a[i] - a[i - 1];
      }
      check(i);
      continue;
    }
    if (a[i - 1] != -1 && a[i] - a[i - 1] == dif) q[i] = res, q[i - 1] = res;
    if (p != 0 && q[als[p - 1].second] == 0) {
      dif = (als[p].first - als[p - 1].first) /
            (als[p].second - als[p - 1].second);
      q[i] = ++res;
      q[als[p - 1].second] = res;
    }
    check(i);
  }
  cout << res;
  return 0;
}
