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 int maxn = 2e5;
long long line[maxn];
int sum, q1, q2;
int flag1, k, qw, wa, flag2;
int main() {
  int n, zz = 1;
  cin >> n;
  for (int i = (int)(1); i < (int)(n + 1); i++) cin >> line[i];
  while (zz <= n) {
    q1 = 0, q2 = 0, flag1 = 0, k = 0, wa = 0, flag2 = 0;
    sum++;
    for (int i = (int)(zz); i < (int)(n + 1); i++) {
      qw = i;
      if (line[i] != -1 && flag1 == 0) {
        q1 = line[i];
        flag1 = 1;
        continue;
      }
      if (flag1 == 1 && line[i] == -1) {
        k++;
        continue;
      }
      if (line[i] == -1 && flag1 == 0) {
        wa++;
        continue;
      }
      if (line[i] != -1 && flag1 == 1) {
        q2 = line[i];
        flag2 = 1;
        break;
      }
    }
    zz = qw;
    if (qw > n) break;
    if (qw == n && (flag2 == 0 || flag1 == 0)) break;
    if ((q2 - q1) % (k + 1) != 0) continue;
    long long d = (q2 - q1) / (k + 1);
    if (q1 - wa * d <= 0) continue;
    zz = qw + 1;
    while (zz <= n) {
      if (line[zz] == -1) {
        if (line[zz - 1] + d <= 0) break;
        line[zz] = line[zz - 1] + d;
        zz++;
      } else {
        if (line[zz] - line[zz - 1] != d) break;
        zz++;
      }
    }
  }
  cout << sum << endl;
  return 0;
}
