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 <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <ctype.h>
#include <queue>
#include <map>
#include <algorithm>
using namespace std;
#define maxn 300000
#define LL __int64
int a[maxn];
int main()
{
    int n,m;
    while(~scanf("%d",&n))
    {
        for(int i=1; i<=n; i++)scanf("%d",&a[i]);
        int l,r,ans,mid;
        int leap;
        l=r=mid=-1;
        ans=0;
        leap=0;
        int ns=0;
        for(int i=1; i<=n; i++)
        {
            if(a[i]!=-1)
            {
                if(l==-1)l=i;
                else
                {
                    if(mid==-1)
                    {
                        int x=a[i]-a[l];
                        int y=i-l;
                        if(x%y!=0)
                        {
                            l=mid=r=-1;
                            //  cout<<"++"<<i<<endl;
                            ans++;
                            ns=0;
                        }
                        else
                        {
                            mid=x/y;
                            leap=1;
                            LL last=(LL)a[l]-(LL)mid*ns;
                            if(last<=0)
                            {
                                ans++;
                                l=mid=r=-1;
                                ns=0;
                            }
                            else
                            {
                                if(mid<0)
                                {
                                    leap=-1;
                                    mid=-mid;
                                }
                                l=i;
                            }
                        }
                    }
                    else
                    {
                        int x=a[i]-a[l];
                        int y=i-l;
                        int z=x/y;
                        z=z*leap;
                        if(z==mid)
                        {
                            l=i;
                        }
                        else
                        {
                            l=i;
                            mid=r=-1;
                            ans++;
                            ns=0;
                        }
                    }
                }
            }
            else
            {
                if(l==-1)ns++;
                if(mid!=-1&&leap==-1)
                {
                    int us=a[l]+(i-l)*mid*leap;
                    if(us<=0)
                    {
                        ans++;
                        l=r=mid=-1;
                        ns=0;
                    }
                }
            }
        }
        ans++;
        cout<<ans<<endl;
    }
    return 0;
}















