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 Set(long long N, long long pos) { return N = N | (1 << pos); }
long long reset(long long N, long long pos) { return N = N & ~(1 << pos); }
bool check(long long N, long long pos) { return (bool)(N & (1 << pos)); }
void CI(long long &_x) { scanf("%d", &_x); }
void CO(long long &_x) { cout << _x; }
template <typename T>
void getarray(T a[], long long n) {
  for (long long i = 0; i < n; i++) cin >> a[i];
}
template <typename T>
void prLLIarray(T a[], long long n) {
  for (long long i = 0; i < n - 1; i++) cout << a[i] << " ";
  cout << a[n - 1] << endl;
}
const double EPS = 1e-9;
const long long INF = 0x7f7f7f7f;
long long dr8[8] = {1, -1, 0, 0, 1, -1, -1, 1};
long long dc8[8] = {0, 0, -1, 1, 1, 1, -1, -1};
long long dr4[4] = {0, 0, 1, -1};
long long dc4[4] = {-1, 1, 0, 0};
long long kn8r[8] = {1, 2, 2, 1, -1, -2, -2, -1};
long long kn8c[8] = {2, 1, -1, -2, -2, -1, 1, 2};
int main() {
  int n, b = 0;
  cin >> n;
  vector<int> V;
  for (int i = 0; i < n; i++) {
    int temp;
    cin >> temp;
    if (temp == -1 && b == 0) continue;
    b = 1;
    V.push_back(temp);
  }
  while (V.size() > 0 && V[V.size() - 1] == -1) {
    V.pop_back();
  }
  n = V.size();
  if (n == 0) {
    puts("1");
    return 0;
  }
  int dif = 1 << 30;
  int ans = 0, temp = V[V.size() - 1], kk = 1;
  V.pop_back();
  while (V.size() > 0) {
    int last = V[V.size() - 1];
    if (last == -1) {
      kk++;
    } else if (dif == 1 << 30) {
      kk = 1;
      dif = (temp - last) / kk;
    } else if (temp - (dif * kk) == last) {
      kk = 1;
    } else {
      ans++;
      kk = 1;
      dif = 1 << 30;
    }
    temp = last;
    V.pop_back();
  }
  cout << ans + 1 << "\n";
}
