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>
#pragma comment(linker, "/STACK:102400000,102400000")
using namespace std;
template <class _T>
inline _T loww(_T n) {
  return n & (-n);
}
template <class _T>
inline void swapp(_T &x, _T &y) {
  _T t;
  t = x, x = y, y = t;
}
template <class _T>
inline _T minn(_T i, _T j) {
  return i > j ? j : i;
}
template <class _T>
inline _T maxx(_T i, _T j) {
  return i > j ? i : j;
}
template <class _T>
inline _T gcd(_T b, _T c) {
  return b && c ? (c ? gcd(c, b % c) : b) : b | c;
}
template <class _T>
inline _T abss(_T b) {
  return b > 0 ? b : -b;
}
int a[200005];
int state = 0;
int x = 0, y = 0, z = 0, s = 1;
int main() {
  int n, i, t1;
  scanf("%d", &n);
  for (i = 0; i < n; i++) {
    scanf("%d", &a[i]);
  }
  for (i = 0; i < n; i++) {
    if (state == 0) {
      if (a[i] == -1)
        y++;
      else {
        x = a[i];
        state = 1;
      }
    } else if (state == 1) {
      if (a[i] == -1)
        z++;
      else {
        t1 = a[i] - x;
        if (t1 % (z + 1) == 0) {
          t1 /= z + 1;
          if (x - t1 * y >= 1) {
            state = 2;
            x = t1;
            y = a[i];
          } else {
            s++;
            x = a[i];
            y = z = 0;
          }
        } else {
          s++;
          x = a[i];
          y = z = 0;
        }
      }
    } else {
      t1 = y + x;
      if (t1 >= 1 && (a[i] == -1 || a[i] == t1)) {
        y = t1;
      } else {
        s++;
        x = y = z = 0;
        i--;
        state = 0;
      }
    }
  }
  printf("%d\n", s);
  return 0;
}
