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;
const long long INF = LONG_MAX >> 1;
int n, now, ans, now1, now2;
long long x1, x2, d, a[200005];
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%I64d", &a[i]);
  now = 1;
  d = INF;
  while (now <= n) {
    ans++;
    if (a[now] == -1) {
      now1 = now;
      while (now1 <= n && a[now1] == -1) now1++;
      x1 = x2 = INF;
      if (now1 <= n) x1 = a[now1];
      now2 = now1 + 1;
      while (now2 <= n && a[now2] == -1) now2++;
      if (now2 <= n) x2 = a[now2];
      if (x2 == INF)
        break;
      else {
        if ((x2 - x1) % (now2 - now1) != 0 ||
            ((x1 < x2) && now1 - now > (x1 - 1) / (x2 - x1)))
          now = now2;
        else {
          d = (x2 - x1) / (now2 - now1);
          now = now2 + 1;
          while (now <= n) {
            if (a[now] == -1 && a[now - 1] + d > 0) a[now] = a[now - 1] + d;
            if (a[now] == a[now - 1] + d && a[now - 1] + d > 0)
              now++;
            else
              break;
          }
        }
      }
    } else {
      if (now + 1 > n) break;
      if (a[now + 1] != -1) {
        d = a[now + 1] - a[now];
        now++;
        while (now <= n) {
          if (a[now] == -1 && a[now - 1] + d > 0) a[now] = a[now - 1] + d;
          if (a[now] == a[now - 1] + d && a[now - 1] + d > 0)
            now++;
          else
            break;
        }
      } else {
        x1 = INF;
        now1 = now + 1;
        while (now1 <= n && a[now1] == -1) now1++;
        if (now1 > n) break;
        if ((a[now1] - a[now]) % (now1 - now) == 0) {
          d = (a[now1] - a[now]) / (now1 - now);
          now = now1 + 1;
          while (now <= n) {
            if (a[now] == -1 && a[now - 1] + d > 0) a[now] = a[now - 1] + d;
            if (a[now] == a[now - 1] + d && a[now - 1] + d > 0)
              now++;
            else
              break;
          }
        } else
          now = now1;
      }
    }
  }
  printf("%d\n", ans);
  return 0;
}
