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 n, a[200005], k[5], sp, pos1, d, i, ans, nxt, t;
bool f;
long long AB(long long x) { return x > 0 ? x : -x; }
int main() {
  scanf("%I64d", &n);
  for (i = 0; i < n; i++) {
    scanf("%I64d", &a[i]);
  }
  for (i = 0; i < n; i++) {
    if (a[i] == -1) {
      k[t]++;
    } else {
      if (t) {
        sp = AB(a[i] - a[pos1]);
        if (sp / (i - pos1) * (i - pos1) == sp) {
          d = (a[i] - a[pos1]) / (i - pos1);
          if (d > 0) {
            if (a[pos1] - k[0] * d <= 0) {
              ans++;
              i--;
              t = 0;
              k[0] = 0;
              k[1] = 0;
              continue;
            }
          }
          nxt = a[i] + d;
          i++;
          f = true;
          if (nxt <= 0) {
            i--;
            ans++;
            f = false;
          }
          while (f) {
            if (i >= n) {
              ans++;
              break;
            }
            if (a[i] == nxt || a[i] == -1) {
              nxt = nxt + d;
              if (nxt <= 0) {
                ans++;
                break;
              }
              i++;
            } else {
              i--;
              ans++;
              break;
            }
          }
          t = 0;
          k[0] = 0;
          k[1] = 0;
        } else {
          ans++;
          i--;
          t = 0;
          k[0] = 0;
          k[1] = 0;
        }
      } else {
        pos1 = i;
        t++;
      }
    }
  }
  if (k[0] == 0 && t == 0)
    printf("%I64d", ans);
  else
    printf("%I64d", ans + 1);
  return 0;
}
