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>
long long a[200001];
int main() {
  int i, j, k;
  int n;
  int ans;
  long long diff;
  bool first;
  const long long LLMAX = (long long)((1llu << 63) - 1);
  while (scanf("%d", &n) == 1) {
    ans = 0;
    for (i = 0; i < n; i++) {
      scanf("%I64d", &a[i]);
    }
    first = false;
    diff = LLMAX;
    for (i = 0; i < n; i++) {
      if (first) {
        if (a[i] == -1) {
          if (diff != LLMAX) {
            if (a[i - 1] + diff > 0) {
              a[i] = a[i - 1] + diff;
              continue;
            }
          } else {
            for (j = i + 1; j < n && a[j] == -1; j++)
              ;
            if (j < n && (a[j] - a[i - 1]) % (j - (i - 1)) == 0) {
              diff = (a[j] - a[i - 1]) / (j - (i - 1));
              while (++i < j) a[i] = a[i - 1] + diff;
              continue;
            } else {
              i = n;
              continue;
            }
          }
        } else {
          if (diff == LLMAX) {
            diff = a[i] - a[i - 1];
            continue;
          } else if (diff == a[i] - a[i - 1]) {
            continue;
          }
        }
      }
      if (a[i] == -1) {
        ans++;
        for (j = i + 1; j < n && a[j] == -1; j++)
          ;
        for (k = j + 1; k < n && a[k] == -1; k++)
          ;
        if (j == n || k == n) {
          break;
        }
        if ((a[k] - a[j]) % (k - j) == 0 &&
            a[j] - (a[k] - a[j]) / (k - j) * j > 0) {
          i = k;
          first = true;
          diff = (a[k] - a[j]) / (k - j);
        } else {
          i = k - 1;
          first = false;
        }
        continue;
      }
      first = true;
      diff = LLMAX;
      ans++;
    }
    printf("%d\n", ans);
  }
}
