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 long long MOD = 1e9 + 7;
const int INF = 2e9;
const long long INF64 = 3e18;
const long double EPS = 1e-12;
const long double PI = 3.1415926535897932384626433832795028841;
const long long MD = 925262732;
const long long T = 634521;
const int N = 200100;
const int M = 2001;
long long n, a[N];
vector<pair<long long, long long> > p;
int main() {
  cin >> n;
  for (int i = 0; i < int(n); i++) {
    scanf("%I64d", &a[i]);
  }
  long long ans = 0;
  for (int i = 0; i < n; i++) {
    p.clear();
    long long j = i;
    long long q = 1;
    while (j < n) {
      if (a[j] != -1) {
        if (int((p).size()) == 0)
          p.push_back(make_pair(a[j], j));
        else {
          if (int((p).size()) == 1) {
            p.push_back(make_pair(a[j], j));
            q = p[1].first - p[0].first;
            long long z = p[1].second - p[0].second;
            if (abs(q) % z != 0) break;
            q /= z;
            if (p[0].first - q * (p[0].second - i) <= 0) break;
          } else {
            p.push_back(make_pair(a[j], j));
            long long qq =
                p[int((p).size()) - 1].first - p[int((p).size()) - 2].first;
            long long z =
                p[int((p).size()) - 1].second - p[int((p).size()) - 2].second;
            if (abs(qq) % z != 0 || qq / z != q) break;
          }
        }
      } else {
        if (int((p).size()) > 1) {
          long long z = int((p).size()) - 1;
          if (p[z].first + q * (j - p[z].second) <= 0) break;
        }
      }
      j++;
    }
    ans++;
    i = j - 1;
  }
  cout << ans;
  return 0;
}
