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 INF = 2000 * 1000 * 1000;
int main() {
  freopen("input.txt", "r", stdin);
  int n;
  scanf("%d", &n);
  int num = 1;
  bool is_start = true, is_start2 = true, last1 = true;
  int first_n1 = -1, n1val = -1, lastval = -1, potent = 0;
  int first = -1, second = -1;
  int nn = 0, d = INF;
  for (int i = 0; i < n; i++) {
    int x;
    scanf("%d", &x);
    if (x == -1 && is_start)
      continue;
    else
      is_start = false;
    nn++;
    if (x != -1) {
      lastval = x;
      potent = 0;
      last1 = true;
      if (first_n1 == -1) {
        first_n1 = i;
        n1val = x;
      }
      second = x;
      if (first == -1) {
        first = second;
        nn = 0;
        continue;
      }
      if ((second - first) % nn == 0 &&
          (d == INF || (second - first) == nn * d)) {
        d = (second - first) / nn;
        if (is_start2) {
          if (n1val - d * first_n1 <= 0) {
            num++;
          }
          is_start2 = false;
        }
        first = x;
        nn = 0;
        continue;
      } else {
        num++;
        d = INF;
        nn = 0;
        first = x;
      }
    } else {
      if (d != INF) {
        lastval += d;
      }
      if (lastval <= 0) {
        potent = 1;
      }
    }
  }
  cout << num + potent << endl;
  return 0;
}
