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 N = 200005;
const int INF = 1e9 + 7;
const int MOD = 1e9 + 7;
const double eps = 1e-6;
const double pi = acos(-1.0);
vector<pair<int, int> > v;
long long a[N];
int b[N], used[N];
int main() {
  int l = 0, n, L = 0, R;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%I64d", &a[i]);
    if (a[i] != -1) {
      if (l) v.push_back(make_pair(l, i));
      l = i;
      R = i;
      if (!L) L = i;
    }
  }
  if (!L || L == R) {
    puts("1");
    return 0;
  }
  int ans = 0;
  for (int i = 0; i < v.size(); i++) {
    int x = v[i].first, y = v[i].second;
    if (abs(a[x] - a[y]) % (y - x) == 0) {
      ans++;
      if (b[x] == 1) {
        ans--;
        if (a[x] - a[x - 1] != (a[x] - a[y]) / (x - y)) continue;
      }
      used[i] = 1;
      for (int j = x; j <= y; j++) {
        b[j] = 1;
        a[j] = (long long)(j - x) * (a[y] - a[x]) / (y - x) + a[x];
      }
    }
  }
  for (int i = 0; i < v.size(); i++)
    if (!used[i]) {
      int x = v[i].first, y = v[i].second, l = y - x - 1;
      if (b[x]) {
        for (int j = x + 1; j < y; j++) {
          a[j] = (a[x] - a[x - 1]) + a[j - 1];
          if (a[j] <= 0) break;
          l--;
          b[j] = 1;
        }
      }
      if (b[y]) {
        for (int j = y - 1; j > x; j--) {
          if (b[j]) break;
          a[j] = (a[j] - a[j + 1]) + a[j + 1];
          if (a[j] <= 0) break;
          l--;
          b[j] = 1;
        }
      }
      if (l || !b[x] || !b[y]) ans++;
      if (!b[x] && !b[y]) ans++;
    }
  if (L > 1) {
    if (a[L] + (long long)(L - 1) * (a[L] - a[L + 1]) <= 0) ans++;
  }
  if (R < n) {
    if (a[R] + (long long)(n - R) * (a[R] - a[R - 1]) <= 0) ans++;
  }
  cout << ans << endl;
}
