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 sequence[200000 + 1];
int main() {
  int n, first = -1, sec = -1, iter, begseq = -1, count = 0;
  long long delta = 100000000;
  bool seqnotfinished = false;
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> sequence[i];
  iter = 1;
  while (iter <= n) {
    if (sequence[iter] == -1 && begseq == -1)
      begseq = iter;
    else {
      if (sequence[iter] != -1 && first == -1)
        first = iter;
      else if (sequence[iter] != -1) {
        if (delta == 100000000) {
          if (abs(sequence[iter] - sequence[first]) % (iter - first) != 0) {
            begseq = -1;
            first = iter;
            ++count;
            ++iter;
            continue;
          } else {
            delta = (sequence[iter] - sequence[first]) / (iter - first);
            if (begseq < first && begseq != -1) {
              if (sequence[first] - delta * (first - begseq) < 1) {
                begseq = -1;
                first = iter;
                delta = 100000000;
                ++count;
                ++iter;
                continue;
              }
            }
            begseq = -1;
            first = iter;
            ++iter;
            continue;
          }
        } else {
          if (sequence[first] + delta * (iter - first) == sequence[iter]) {
            begseq = -1;
            first = iter;
            ++iter;
            continue;
          } else if (delta > 0) {
            begseq = -1;
            first = iter;
            ++count;
            delta = 100000000;
            ++iter;
            continue;
          } else {
            if (delta != 0)
              begseq = first + (sequence[first] - 1) / abs(delta);
            else
              begseq = -1;
            if (begseq >= iter) begseq = -1;
            if (begseq != -1) {
              begseq++;
              if (begseq == iter) begseq = -1;
            }
            first = iter;
            ++count;
            delta = 100000000;
            ++iter;
            continue;
          }
        }
      }
    }
    ++iter;
  }
  if (first <= n) {
    if (delta == 100000000 || first == n)
      ++count;
    else if (sequence[first] + (iter - first - 1) * delta < 1)
      count += 2;
    else
      ++count;
  }
  cout << count;
  return 0;
}
