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<set>
#include<queue>
#include<vector>
#include<map>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
using namespace std;

#define Max(a,b) (a>b?a:b)
#define Min(a,b) (a<b?a:b)
#define Mem(a,b) (memset(a,b,sizeof(a)))
#define inf 1000000009
#define N 200005
typedef __int64 ll;
ll s[N];

int main()
{

	int j,i,k;
	int p;
	int n;
	int a,b,c;
	scanf("%d",&n);
	for( i= 1; i<= n ; i++ )
		scanf("%I64d", &s[i] );
	int sum = 0;
	for(i= 1; i<= n ;)
	{
		p =inf;
		a= i;
		if(s[i]==-1) a=-1;
		for( j= i+1; j<= n ; j++  )
		{
			if( p == inf )
			{
				if(s[j] == -1)
					continue;
				else
				{
					if(a==-1)
						a=j;
					else
					{
						if( (s[j] - s[a] ) % ( j-a ) == 0)
						{
							p =(s[j] - s[a] ) / ( j-a );
							if(s[a] - p* ( a-i ) <= 0 ) break;
						}
						else
							break;
					}// else
				}//else
			}// if
			else
			{
				if(s[j] == -1)
				{
					if(s[a] + p* ( j-a ) <= 0 ) break;
				}
				else
				{
					if(s[a] + p* ( j-a ) <= 0 ) break;
					if( s[j] != s[a] + p*(j-a)) break;
				}

			}//else
		}//for
		sum++, i=j;
	}
	cout<<sum<<endl;
	return 0;
}