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[200000], d;
int n, m, i, j, k;
bool bb[200000], ab[200000], b, f = 1, bd, ff;
int main() {
  scanf("%d", &n);
  for (i = 0; i < n; i++) scanf("%I64d", &a[i]);
  for (i = 0; i < n; i++)
    if (~a[i]) ++k, d = a[i];
  if (k > 1) {
    while (f) {
      f = 0, b = 0, bd = 0, ff = 1;
      for (i = 0; ff && i < n; i++) {
        if (~a[i]) {
          if (b) {
            if (bd) {
              if (a[i] != a[i - 1] + d) bd = 0, k = i;
            } else {
              if ((a[i] - a[k]) % (i - k) == 0) {
                d = (a[i] - a[k]) / (i - k);
                bd = 1;
                for (j = k + 1; j < i; j++) a[j] = a[j - 1] + d;
                for (j = k - 1; j >= 0 && !~a[j]; j--) {
                  a[j] = a[j + 1] - d;
                  if (a[j] < 1) {
                    a[j] = a[j + 1];
                    ff = 0;
                    f = 1;
                    break;
                  }
                }
              } else {
                for (j = k + 1; j < i; j++) a[j] = a[k];
                for (j = k - 1; j >= 0 && !~a[j]; j--) a[j] = a[k];
              }
            }
          } else
            b = 1, k = i;
        } else {
          if (bd) {
            a[i] = a[i - 1] + d;
            if (a[i] < 1) {
              if (bb[i]) {
                a[i] = -1;
                for (j = i; j < n && !~a[j]; j++) a[j] = a[i - 1];
                i = j;
              } else
                a[i] = -1, bb[i] = 1, bd = 0, b = 0, f = 1;
            }
          } else {
            if (ab[i] && i) a[i] = a[i - 1];
            ab[i] = 1;
            f = 1;
          }
        }
      }
    }
  } else {
    if (!k) d = 1;
    for (i = 0; i < n; i++) a[i] = d;
  }
  m = 1;
  for (i = 2; i < n; i++)
    if (a[i] - a[i - 1] != a[i - 1] - a[i - 2]) ++m, ++i;
  printf("%d\n", m);
  return 0;
}
