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 solve(vector<pair<long long, long long> > solvable, long long idx,
                long long j = 0) {
  long long n = solvable.size();
  if (solvable.size() - idx <= 1) return 1;
  long long base = solvable[idx].first;
  long long to = solvable[idx + 1].first;
  if (abs(to - base) % solvable[idx].second != 0) {
    return 1 + solve(solvable, idx + 1);
  }
  long long step = (to - base) / solvable[idx].second;
  long long check = idx + 2;
  while ((check < n) &&
         (solvable[check].first ==
          solvable[check - 1].first + step * solvable[check - 1].second))
    check++;
  long long next =
      solvable[check - 1].first + step * (solvable[check - 1].second - 1);
  bool cond = (false && j && (solvable[idx].first - step * j <= 0));
  if (check == n)
    if (next > 0)
      return 1 + cond;
    else
      return 2 + cond;
  return 1 + solve(solvable, check) + cond;
}
int main() {
  long long n;
  scanf("%lld", &n);
  long long *arr = new long long[200005];
  for (long long i = 0; i < n; i++) {
    scanf("%lld", &arr[i]);
  }
  vector<pair<long long, long long> > solvable;
  int i = 0;
  int j = 0;
  while (i < n && arr[i] == -1) {
    j++;
    i++;
  }
  while (i < n) {
    long long a = arr[i];
    long long ct = 1;
    while (i < n && arr[i] == -1) {
      i++;
      ct++;
    }
    solvable.push_back(make_pair(a, ct));
    i++;
  }
  long long ans = solve(solvable, 0, j);
  printf("%lld\n", ans);
}
