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;
int a[100009], v1[100009], v2[100009], n, ans = 0;
int left(int i, int staep, int expc);
int right(int i, int step, int expc);
int get_nxt(int i);
int t;
int main() {
  memset(v1, 0, sizeof(v1));
  memset(v2, 0, sizeof(v2));
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", &a[i]);
  int ans = 0;
  for (int i = 0; i < n - 1; i++) {
    int j = i + 1;
    if (a[i] != -1 && a[j] != -1 && !v1[i]) {
      int tmp = right(i, a[j] - a[i], a[i]);
      tmp += left(j, a[i] - a[j], a[j]);
      if (tmp) ans++;
    }
  }
  int j = 0;
  for (int i = 0; i < n; i++)
    if (v1[i] == 0) v2[j++] = a[i];
  t = j;
  int prev = 0, accum = 0;
  for (int i = 0; i < j; i++) {
    if (a[i] == -1)
      accum++;
    else {
      int tmp = get_nxt(i);
      if (tmp != -1) {
        if ((a[tmp] - a[i]) % (tmp - i) == 0) {
          int step = (a[tmp] - a[i]) / (tmp - i);
          if (a[i] - accum * step >= 0)
            ans++;
          else
            ans += 2;
          i = tmp;
        } else {
          int m = min(tmp - i, accum);
          if (a[i] - m >= 0)
            ans++;
          else
            ans += 2;
          i = tmp;
        }
      } else {
        int m = min(n - i, accum);
        if (a[i] - m >= 0)
          ans++;
        else
          ans += 2;
        break;
      }
    }
  }
  printf("%d\n", ans);
  return 0;
}
int get_nxt(int i) {
  for (int j = i + 1; j < t; j++)
    if (v2[j] != -1) return j;
  return -1;
}
int right(int i, int step, int expc) {
  if (i == n || i < 0 || expc < 0) return 0;
  if (v1[i]) return 0;
  if (a[i] == -1 || a[i] == expc) {
    a[i] = expc;
    v1[i] = 1;
    return right(i + 1, step, expc + step) + 1;
  }
  return 0;
}
int left(int i, int step, int expc) {
  if (i == n || i < 0 || expc < 0) return 0;
  if (v1[i]) return 0;
  if (a[i] == -1 || a[i] == expc) {
    v1[i] = 1;
    a[i] = expc;
    return left(i - 1, step, expc + step) + 1;
  }
  return 0;
}
