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;
inline void read(int &x) {
  short negative = 1;
  x = 0;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') negative = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9')
    x = (x << 3) + (x << 1) + (c ^ 48), c = getchar();
  x *= negative;
}
long long quickpower(long long n, long long k) {
  long long ans = 1;
  while (k) {
    if (k % 2) {
      ans *= n;
      ans %= 1000000007;
    }
    n *= n;
    n %= 1000000007;
    k /= 2;
  }
  return ans;
}
string int_to_string(int n) {
  string s = "";
  while (n) {
    int now = n % 10;
    s += now + '0';
    n /= 10;
  }
  reverse(s.begin(), s.end());
  return s;
}
int string_to_int(string s) {
  int n = 0;
  for (int i = 0, _n = s.size(); i < s.size(); i++) {
    n *= 10;
    n += s[i] - '0';
  }
  return n;
}
int n;
long long a[200100];
pair<int, int> p[200100];
int now = 0, last = 0;
bool f;
int main() {
  ios::sync_with_stdio(0);
  cin >> n;
  for (int i = 0, _n = n; i < n; i++) cin >> a[i];
  int cnt = 0;
  for (int i = 0, _n = n; i < n; i++)
    if (a[i] != -1) cnt++;
  if (cnt <= 1) {
    cout << 1 << endl;
    return 0;
  }
  for (int i = 0, _n = n + 1; i < n + 1; i++) {
    if (a[i] != -1) {
      if (i == n - 1) {
        now++;
        break;
      }
      for (int j = (i + 1), _b = (n - 1); j <= _b; j++) {
        if (j == n - 1 && a[j] == -1) {
          now++;
          i = j;
          break;
        }
        if (a[j] != -1) {
          int mm = a[j] - a[i];
          int m = abs(a[j] - a[i]);
          mm = mm / (j - i);
          m = m * 100 / (j - i);
          if (m % 100) {
            p[now].first = last;
            p[now].second = j;
            i = j - 1;
            last = j;
            now++;
          } else {
            if (a[i] - (i - last) * mm <= 0) {
              p[now].first = last;
              p[now].second = j;
              last = j;
              i = j - 1;
              now++;
            } else {
              int k;
              for (k = j + 1; k < n; k++) {
                if (a[k] == -1) a[k] = a[k - 1] + mm;
                if (a[k] <= 0) {
                  a[k] = -1;
                  break;
                }
                if (a[k] - a[k - 1] != mm) {
                  break;
                }
              }
              p[now].first = last;
              p[now].second = k;
              i = k - 1;
              last = k;
              now++;
              break;
            }
          }
        }
      }
    }
  }
  cout << now << endl;
  return 0;
}
