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 int INF = 2999999999LL;
struct DUAN {
  int id;
  long long int first, second;
  int stpos;
  long long int ddd;
};
int n;
long long a[320000];
int one[320000];
long long int ABS(long long int x) {
  if (x < 0L) return -x;
  return x;
}
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  int last = -1;
  for (int i = 0; i < n; i++) {
    if (a[i] != -1LL) {
      one[i] = i - last - 1;
      last = i;
    }
  }
  int cnt = 0;
  bool FST = true;
  vector<DUAN> duan;
  for (int i = 0; i < n; i++) {
    if (a[i] == -1) continue;
    if (FST) {
      duan.push_back((DUAN){cnt, a[i], -998, i, -9989});
      FST = false;
    } else {
      if (duan[cnt].second == -998) {
        int dlen = i - duan[cnt].stpos;
        if (ABS(a[i] - duan[cnt].first) % dlen == 0) {
          long long int D = (a[i] - duan[cnt].first) / dlen;
          int numone = one[duan[cnt].stpos];
          long long int xxx =
              duan[cnt].first - (long long int)numone * (long long int)D;
          if (xxx <= 0LL) {
            one[i] = 0;
            duan.push_back((DUAN){++cnt, a[i], -998, i, -9989});
          } else {
            duan[cnt].second = a[i];
            duan[cnt].ddd = D;
          }
        } else {
          one[i] = 0;
          duan.push_back((DUAN){++cnt, a[i], -998, i, -9989});
        }
      } else {
        int dlen = i - duan[cnt].stpos;
        long long int xxx = duan[cnt].first + duan[cnt].ddd * dlen;
        if (xxx <= 0 || xxx != a[i]) {
          if (xxx <= 0) {
            int deone = duan[cnt].second / abs(duan[cnt].ddd);
            one[i] = max(one[i] - deone, 0);
          } else
            one[i] = 0;
          duan.push_back((DUAN){++cnt, a[i], -998, i, -9989});
        }
      }
    }
  }
  int temp = 0;
  if ((int)duan.size() > 0) {
    if (duan[cnt].ddd != -9989) {
      int d = duan[cnt].ddd;
      if (d < 0) {
        int dlen = (n - 1) - duan[cnt].stpos;
        long long int xxx = (long long int)duan[cnt].first +
                            (long long int)d * (long long int)dlen;
        if (xxx <= 0LL) temp++;
      }
    }
  }
  printf("%d\n", max(1, temp + (int)duan.size()));
  return 0;
}
