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 int maxn = 222222;
struct obj {
  int need, pay;
  int id;
} request[maxn];
struct objp {
  int cap, v;
  int id;
} table[maxn];
bool operator<(obj a, obj b) { return a.pay > b.pay; }
bool operator<(objp a, objp b) { return a.cap < b.cap; }
int arr[maxn];
int main() {
  int n, k;
  while (~scanf("%d", &n)) {
    for (int i = 1; i <= n; i++) scanf("%d", &arr[i]);
    int status = 0, add = 0, num = 0, nump = 0, cach = 0;
    int res = 0;
    for (int i = 1; i <= n; i++) {
      switch (status) {
        case 0:
          if (arr[i] == -1) {
            num++;
          } else {
            cach = arr[i];
            status = 1;
            nump = 0;
          }
          break;
        case 1:
          if (arr[i] == -1) {
            nump++;
          } else {
            if ((arr[i] - cach) % (nump + 1) == 0) {
              status = 2;
              add = (arr[i] - cach) / (nump + 1);
              if (add > 0 && cach - add * num <= 0) res += 1;
              cach = arr[i];
            } else {
              cach = arr[i];
              res++;
              num = nump = 0;
            }
          }
          break;
        case 2:
          if (arr[i] == -1) {
            if (add + cach <= 0) {
              num = 1;
              status = 0;
              res++;
            } else {
              cach += add;
            }
          } else {
            if (cach + add == arr[i]) {
              cach += add;
            } else {
              cach = arr[i];
              status = 1;
              nump = num = 0;
              res++;
            }
          }
          break;
      }
    }
    res++;
    printf("%d\n", res);
  }
  return 0;
}
