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>
long long n, i, tot, b[1000000], o[1000000], z, q, j, ans;
long long tmp, a[1000000], sum;
int main() {
  scanf("%lld", &n);
  for (i = 1; i <= n; i++) {
    scanf("%lld", &a[i]);
    if (a[i] != -1) {
      tot++;
      b[tot] = i;
    } else {
      if (tot == 0) sum++;
    }
    o[i] = 0x37373738;
  }
  tmp = b[1];
  for (i = 2; i <= tot; i++)
    if ((a[b[i]] - a[b[i - 1]]) % (b[i] - b[i - 1]) == 0) {
      z = (a[b[i]] - a[b[i - 1]]) / (b[i] - b[i - 1]);
      if ((o[b[i - 1]] == 0x37373738) || (o[b[i - 1]] == z)) {
        if ((b[i - 1] != tmp) ||
            ((b[i - 1] == tmp) && (a[b[i - 1]] - sum * z > 0))) {
          o[b[i - 1]] = z;
          o[b[i]] = z;
        } else {
          sum = b[i] - b[i - 1] - 1;
          tmp = b[i];
        }
      } else {
        sum = b[i] - b[i - 1] - 1;
        tmp = b[i];
      }
    } else {
      sum = b[i] - b[i - 1] - 1;
      tmp = b[i];
    }
  for (i = 1; i <= tot; i++)
    if (o[b[i]] == 0x37373738) o[b[i]] = 0;
  b[tot + 1] = n + 1;
  for (i <= tot; i >= 1; i--) {
    tmp = a[b[i]];
    q = o[b[i]];
    for (j = b[i] - 1; j > b[i - 1]; j--) {
      tmp = tmp - q;
      if (tmp <= 0) break;
      a[j] = tmp;
      o[j] = q;
    }
    tmp = a[b[i]];
    q = o[b[i]];
    for (j = b[i] + 1; j < b[i + 1]; j++) {
      tmp = tmp + q;
      if (tmp <= 0) break;
      a[j] = tmp;
      o[j] = q;
    }
  }
  for (i = 1; i <= n; i++) {
    o[i] = 0;
    if (a[i] == -1) a[i] = 1;
  }
  ans = 1;
  for (i = 2; i <= n; i++) {
    if (o[i - 1] == 0) {
      tmp = a[i] - a[i - 1];
      o[i] = 1;
    } else {
      if (a[i] - a[i - 1] != tmp)
        ans++;
      else
        o[i] = 1;
    }
  }
  printf("%lld\n", ans);
  scanf("\n");
}
