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 bfsz = 1 << 16;
char bf[bfsz + 5];
int rsz = 0;
int ptr = 0;
char gc() {
  if (rsz <= 0) {
    ptr = 0;
    rsz = fread(bf, 1, bfsz, stdin);
    if (rsz <= 0) return EOF;
  }
  --rsz;
  return bf[ptr++];
}
void ga(char &c) {
  c = EOF;
  while (!isalpha(c)) c = gc();
}
int gs(char s[]) {
  int l = 0;
  char c = gc();
  while (isspace(c)) c = gc();
  while (c != EOF && !isspace(c)) {
    s[l++] = c;
    c = gc();
  }
  s[l] = '\0';
  return l;
}
template <class T>
bool gi(T &v) {
  v = 0;
  char c = gc();
  while (c != EOF && c != '-' && !isdigit(c)) c = gc();
  if (c == EOF) return false;
  bool neg = c == '-';
  if (neg) c = gc();
  while (isdigit(c)) {
    v = v * 10 + c - '0';
    c = gc();
  }
  if (neg) v = -v;
  return true;
}
bool exitInput = false;
int ntest = 1, itest = 1;
const int dx[4] = {+0, +1, +0, -1};
const int dy[4] = {+1, +0, -1, +0};
const long long Mod = 1e9 + 7;
const int maxn = 100000 + 5;
const int maxv = 5 + 5;
const int maxe = 4 + 5;
int n, a[maxn];
void pre() {}
void read() {
  scanf("%d", &n);
  int i;
  for (i = 1; i <= n; ++i) {
    scanf("%d", &a[i]);
  }
}
void solve() {
  int i, j, k, d, res = 0, n1, n2, val1, val2, i1, i2, h;
  bool ok;
  for (i = 1; i <= n;) {
    ++res;
    d = val1 = val2 = -2;
    n1 = n2 = 0;
    for (j = i; j <= n && a[j] == -1; ++j, ++n1)
      ;
    if (j > n) break;
    val1 = a[j];
    i1 = j;
    for (++j; j <= n && a[j] == -1; ++j, ++n2)
      ;
    if (j > n) break;
    val2 = a[j];
    i2 = j;
    h = val2 - val1;
    ok = false;
    if (h % (n2 + 1) == 0) {
      d = h / (n2 + 1);
      k = val1 - n1 * d;
      if (k >= 1) {
        ok = true;
        for (++j; j <= n && a[j] - a[j - 1] == d; ++j)
          ;
      }
    }
    i = j;
  }
  printf("%d\n", res);
}
int main() {
  pre();
  for (itest = 1; itest <= ntest; ++itest) {
    read();
    if (exitInput) {
      break;
    }
    solve();
  }
  fclose(stdout);
  fclose(stdin);
  return 0;
}
