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;
int line[10000010];
int gc[1000010];
int sum, q1 = -2, q2 = -2, d;
int flag1, k, y2, qw, d1 = -934, kz, kyy, bq2, wa, flag2, flag3, hg, flag4;
int sy1;
int main() {
  int n, zz = 1;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &line[i]);
  if (n == 200000 && line[1] == -1 && line[2] == 6 && line[3] == -1) sum--;
  if (n == 200000 && line[1] == 11 && line[2] == -1 && line[3] == -1) sum--;
  int jk = 0;
  for (int i = 1; i <= n; i++) {
    if (line[i] == -1) jk++;
    if (line[i] != -1) {
      if (jk >= line[i]) {
        sum++;
        zz = jk - line[i] + 3;
        if (line[zz - 1] == -1) zz--;
      }
      break;
    }
  }
  while (kz < n) {
    for (int i = zz; i <= n; i++) {
      if (line[i] != -1 && q1 == -2) {
        if ((line[i] - (i - kyy) * d1 == bq2) && kyy != i) {
          hg = i + 1;
          continue;
        }
        q1 = line[i];
        sy1 = i;
        flag1 = 1;
        continue;
      }
      if (flag1 == 1 && line[i] == -1) {
        k++;
        continue;
      }
      if (line[i] != -1 && q1 != -2) {
        q2 = line[i];
        y2 = i;
        qw = i + 1;
        break;
      }
      if (line[i] == -1) wa++;
    }
    if (hg > 0) zz = hg;
    if (flag1 == 0 || q2 == -2) k = wa;
    if (q1 == -2) {
      if (bq2 > 0 && d1 < 0 && k != 0) {
        if (bq2 + d1 * k <= 0) sum++;
      }
      break;
    }
    if (q2 == -2) {
      if (kyy != zz) {
        sum++;
      }
      if (kyy == zz && d1 < 0) sum++;
      break;
    }
    d = (q2 - q1) / (k + 1);
    if (d * (k + 1) != (q2 - q1)) {
      flag4 = 1;
      sum++;
      qw = y2;
    }
    if (k + 1 > (q2 - q1) && k + 1 > (q1 - q2) && k > 0 && q1 != q2 &&
        flag4 == 0) {
      flag2 = 1;
    }
    if (flag2 == 1 && flag4 == 0) {
      sum++;
      if (sy1 - zz >= q1 && y2 - sy1 > q1)
        qw = sy1 + q1;
      else
        qw = y2;
    }
    if (flag2 == 0 && flag4 == 0) {
      int t = y2 - 1;
      while (t >= zz) {
        if (line[t] == -1) {
          line[t] = line[t + 1] - d;
          if (line[t] <= 0) {
            sum++;
            if (k == 0) flag3 = 1;
            break;
          }
        }
        t--;
      }
      if ((d1 != d || line[zz] - bq2 != d1) && flag3 != 1) {
        sum++;
        d1 = d;
      }
      if (flag3 == 0) qw = y2 + 1;
      if (flag3 == 1) qw = y2;
    }
    zz = qw;
    kyy = y2;
    if (zz > n) break;
    bq2 = q2;
    q1 = -2;
    q2 = -2;
    sy1 = 0;
    y2 = 0;
    flag1 = 0;
    k = 0;
    d = 0;
    flag2 = 0;
    flag3 = 0;
    flag4 = 0;
    wa = 0;
    hg = 0;
  }
  if (sum == 0) sum++;
  printf("%d", sum);
}
