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;
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return (a / gcd(a, b)) * b; }
long long pwr(long long base, long long p) {
  long long ans = 1;
  while (p) {
    if (p & 1) ans = (ans * base) % (1000000007LL);
    base = (base * base) % (1000000007LL);
    p >>= 1;
  }
  return ans;
}
long long modInv(long long n, long long mod) { return pwr(n, mod - 2); }
int bitCount(int n) {
  int c = 0;
  while (n) {
    c++;
    n &= n - 1;
  }
  return c;
}
const long long UNDEF = (long long)1e13;
vector<pair<long long, int> > arr;
long long isAP(long long val1, long long val2, int dist) {
  if ((val2 - val1) % dist == 0) return (val2 - val1) / dist;
  return UNDEF;
}
int main() {
  int i, n;
  cin >> n;
  for (i = 0; i < n; i++) {
    long long foo;
    cin >> foo;
    if (foo == -1) continue;
    arr.push_back(pair<long long, int>(foo, i));
  }
  if (arr.size() <= 1) {
    cout << "1\n";
    return 0;
  }
  long long ans = 0, d = UNDEF;
  if (arr.back().second < n - 1) ans++;
  long long first = -UNDEF, last;
  for (i = 1; i < arr.size(); i++) {
    if (d == UNDEF) {
      long long x = isAP(arr[i - 1].first, arr[i].first,
                         arr[i].second - arr[i - 1].second);
      if (x == UNDEF)
        ans++;
      else
        d = x;
    } else {
      long long x = isAP(arr[i - 1].first, arr[i].first,
                         arr[i].second - arr[i - 1].second);
      if (x != d) {
        ans++;
        d = UNDEF;
      }
    }
    if (first == -UNDEF) first = d;
    last = d;
  }
  if (first != -UNDEF) {
    int pos = arr[0].second - 1;
    long long val = arr[0].first;
    while (pos > -1) {
      val -= first;
      pos--;
    }
    if (val <= 0) ans++;
  }
  if (last != UNDEF) {
    int pos = arr[arr.size() - 1].second + 1;
    long long val = arr[0].first;
    while (pos < n) {
      val += last;
      pos++;
    }
    if (val <= 0) ans++;
  }
  cout << ans;
  return 0;
}
