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<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
using namespace std;
#define maxn 211111
__int64 num[maxn];
int main()
{
    __int64 n, i, j, l = n+1;
    scanf("%lld",&n);
    for(i=1;i<=n;i++) scanf("%lld",&num[i]);
    l = n+1;
    for(i=1;i<=n;i++)
    {
        if(num[i]!=-1) {l  = i;break;}
    }
    if(l==n+1)
    {
        printf("1\n");
        return 0;
    }
    
    __int64 sum = 1,flag = 0,fc,f = 0,last = 0;
    while(1)
    {
        __int64 r = n+1;
        for(i=l+1;i<=n;i++)
        {
            if(num[i]!=-1){r = i;break;}
        }
        if(r==n+1) {
            if(l!=n)
            {
                if(flag==1)
                {
                    if(num[l]+fc*(n-l)<=0) sum++;
                }
            }
            break;
        }
        
        if(flag)
        {
            if((abs(num[r]-num[l])%(r-l)==0&&(num[r]-num[l])/(r-l)==fc))
            {
                l = r;
            }
            else
            {
            
                last  = r-l-1;
                if(num[l]+last*fc>=1) last = 0;
                flag = 0;
                l = r;
                sum++;
            }
        }
        else
        {
            
            if(abs(num[r]-num[l])%(r-l)==0)
            {
         
                    fc = (num[r]-num[l])/(r-l);
                    if(f==0&&l>1)
                    {
                            if(num[l]-(l-1)*fc<=0){
                                sum++;
                                flag = 0;
                                l = r;
                                f++;
                                continue;
                            } 
                            else
                            {
                                flag  = 1;
                                l = r;
                                f++;
                                continue;
                            }
                    }     
                if(last&&num[l]-fc*last<=0){
                    sum++;
                    flag = last = 0;
                    l = r;
                    continue;
                }
                last = 0; 
                l  =r;
                flag = 1;
                
            }
            else
            {
               l  = r;
               flag = last = 0;
               sum++;
            }
        }
        f++;
    }
    printf("%lld\n",sum);
    return 0;
}