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 a[200010];
int main() {
  int n;
  scanf("%d", &n);
  int is = 0;
  for (int i = (0); i < (n); ++i) {
    scanf("%I64d", &a[i]);
    if (a[i] > 0) is = 1;
  }
  if (is == 0) {
    printf("1\n");
    return 0;
  }
  if (n == 1) {
    printf("1\n");
    return 0;
  }
  int isd = 0;
  long long d = 0;
  int f1 = -1, l1 = -1;
  int last = -1;
  for (int i = (0); i < (n); ++i) {
    if (a[i] < 0) {
      if (f1 == -1) f1 = i;
      l1 = i;
    } else {
      if (isd == 0) {
        if (last == -1) {
          last = i;
        } else {
          long long dy =
              ((a[i] - a[last] > 0) ? a[i] - a[last] : -(a[i] - a[last]));
          int dx = i - last;
          if ((dy % dx) == 0) {
            d = (a[i] - a[last]) / dx;
            bool good = true;
            if (f1 != -1) {
              for (int j = last - 1; j >= f1; --j) {
                if (a[j + 1] - d > 0)
                  a[j] = a[j + 1] - d;
                else {
                  good = false;
                  a[j] = a[j + 1];
                }
              }
              if (good) {
                isd = 1;
                for (int j = last + 1; j <= l1; ++j) a[j] = a[j - 1] + d;
              } else {
                for (int j = f1; j <= l1; ++j) a[j] = a[last];
              }
            } else
              isd = 1;
            l1 = f1 = -1;
          } else {
            if (f1 != -1) {
              for (int j = f1; j <= l1; ++j) {
                a[j] = a[last];
              }
            }
            l1 = f1 = -1;
          }
          last = i;
        }
      } else {
        long long k = d * 1ll * (i - last);
        if (k + a[last] == a[i]) {
          if (f1 != -1)
            for (int j = f1; j <= l1; ++j) a[j] = a[j - 1] + d;
          f1 = l1 = -1;
        } else {
          isd = 0;
          if (f1 != -1) {
            int nf1 = f1;
            for (int j = nf1; j <= l1; ++j) {
              if (a[j - 1] + d > 0) {
                a[j] = a[j - 1] + d;
                f1++;
              } else
                break;
            }
            if (f1 > l1) {
              f1 = l1 = -1;
            }
          }
        }
        last = i;
      }
    }
  }
  if (f1 != -1) {
    if (isd) {
      for (int i = f1; i <= l1; ++i)
        if (a[i - 1] + d > 0)
          a[i] = a[i - 1] + d;
        else
          a[i] = a[i - 1];
    } else
      for (int i = f1; i <= l1; ++i) a[i] = a[last];
  }
  d = a[1] - a[0];
  int res = 1;
  for (int i = (1); i < (n - 1); ++i)
    if (a[i + 1] - a[i] != d) {
      res++;
      d = a[i + 2] - a[i + 1];
    }
  cout << res << endl;
}
