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 <iostream>
#include <string>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>
#include <deque>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <climits>
#include <cctype>
#include <cassert>
using namespace std;

#define rep(i, a, n) 	for (int i=a;i<n;++i)
#define per(i, a, n) 	for (int i=n-1;i>=a;--i)
#define pb 				push_back
#define mp 				make_pair
#define all(x) 			(x).begin(),(x).end()
#define SZ(x) 			((int)(x).size())
#define lson			l, mid, rt<<1
#define rson			mid+1, r, rt<<1|1

const int maxn = 2e5+5;
__int64 a[maxn];

int main() {
	int n;
	int ans = 0;
	__int64 i, j, k;
	__int64 delta, l, r, tmp;

	#ifndef ONLINE_JUDGE
		freopen("data.in", "r", stdin);
		freopen("data.out", "w", stdout);
	#endif

	scanf("%d", &n);
	for (i=0; i<n; ++i)
		scanf("%I64d", &a[i]);

	i = l = 0;
	while (i<n && a[i]==-1)
		++i;
	if (i == n) {
		puts("1");
		return 0;
	}
	while (i < n) {
		j = i;
		++i;
		while (i<n && a[i]==-1)
			++i;
		if (i == n) {
			++ans;
			break;
		}
		k = a[i] - a[j];
		if (k%(i-j) == 0) {
			delta = k / (i-j);
			if (delta > 0) {
				tmp = j - l;
				if (a[j]-tmp*delta <= 0) {
					l = i;
					++ans;	
					continue;
				}
			}
			k = a[i];
			while (k>0 && i<n) {
				if (a[i]==-1 || a[i]==k) {
					++i;
				} else {
					break;
				}
				k += delta;
			}
			if (i == n) {
				++ans;
				break;
			}
			if (k <= 0) {
				l = i;
				while (i<n && a[i]==-1)
					++i;
				if (i == n)
					++ans;
			} else {
				l = i;
			}
		}
		++ans;
	}
	printf("%d\n", ans);

	#ifndef ONLINE_JUDGE
		printf("time = %d.\n", (int)clock());
	#endif

	return 0;
}
