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;
constexpr int N = 2e5 + 9;
int n, a[N], nxt[N], npos[N];
vector<pair<int, int>> nums;
bool vst[N];
int ans;
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) scanf("%d", a + i);
  for (int t = 0; t < 1; ++t) {
    memset(nxt, 0, sizeof nxt);
    memset(npos, 0, sizeof npos);
    nums.clear();
    memset(vst, 0, sizeof vst);
    for (int i = 1, pos = 0, tmp = INT_MAX; i <= n; ++i) {
      if (a[i] != -1) {
        if (pos) {
          npos[pos] = i;
          int delt = a[i] - a[pos];
          int cnt = i - pos;
          if (delt % cnt)
            nxt[pos] = --tmp;
          else
            nxt[pos] = delt / cnt;
        }
        pos = i;
      }
    }
    vst[0] = true;
    for (int i = 1, j; i <= n; i = j + 1) {
      while (a[i] == -1) ++i;
      if (i > n) break;
      int tmp = nxt[i] > 2e9 ? INT_MIN : nxt[i];
      for (j = i; npos[j]; j = npos[j])
        if (nxt[j] != tmp) break;
      nums.emplace_back(i, j);
      memset(vst + i, true, (j - i + 1) * sizeof(int));
      if (i == j) {
        int k;
        for (k = i - 1; !vst[k]; --k) vst[k] = true;
        if (i - k - 1 < a[i])
          for (int k = i + 1; a[k] == -1; ++k) vst[k] = true;
        else
          for (int k = i + 1; a[k] == -1 && k < i + a[i]; ++k) vst[k] = true;
      } else {
        int d = nxt[i];
        for (int k = i - 1; !vst[k] && a[i] > (i - k) * d; --k) vst[k] = true;
        for (int k = j + 1; a[k] == -1 && a[i] > (i - k) * d; ++k)
          vst[k] = true;
      }
    }
    for (int i = 1, j; i <= n; i = j + 1) {
      while (vst[i]) ++i;
      if (i > n) break;
      for (j = i; !vst[j]; ++j)
        ;
      --j;
      nums.emplace_back(i, j);
    }
    ans = max(ans, (int)nums.size());
  }
  printf("%d\n", ans);
  return 0;
}
