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 <fstream>
#include <cstdio>
#include <iomanip>
#include <numeric>
#include <map>
#include <set>
#include <tr1/unordered_map>
#include <tr1/unordered_set>
#include <algorithm>
#include <vector>
#include <cstring>
#include <sstream>
#include <queue>
#include <bitset>
#include <cmath>
using namespace std;
using namespace tr1;

typedef long long lng;

#define F cin
#define G cout

const int K = 1010;
const int N = 200010; 
const int P = 100; 
const int B = 11; 
const int M = 1000000007;

int lst,ans,rat,co,n,a[N];

int main() 
{
	ios::sync_with_stdio(0);
	#ifndef ONLINE_JUDGE
		ifstream F("p.in");
	#endif

	F>>n;
	for (int i=1;i<=n;++i)	
		F>>a[i];
	lst = rat = -1;
	for (int i=1;i<=n;++i)
		if ( a[i] != -1 )
		{
			if ( rat == -1 && lst != -1 )
			{
				if ( (a[i]-lst) % co )
				{
					++ans;
					rat = -1;
				}
				else
				{
					rat = (a[i]-lst) / co;
				}
			}  
			else
				if ( rat != -1 ) 
				{
					if ( (a[i]-lst) % co )
					{
						++ans;
						rat = -1;
					}
					else
						if ( (a[i]-lst) / co != rat )
						{
							++ans;
							rat = -1;
						}
				}
			lst = a[i];
			co = 1;
			//cerr<<ans<<' ';
		}
		else
			co++;
	++ans;
	G<<ans<<'\n';
}
