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<cstdio>
#include<cstring>
#include<algorithm>
#include<cstdlib>
using namespace std;
__int64 a[200005],ans,num,flag,cha=1000000000,wen1,shu1,wei1;
int main(){
    int i,j,m,n;
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        scanf("%I64d",&a[i]);
    }
    wei1=1;
    for(i=1;i<=n;i++){
        if(a[i]==-1){
            if(wei1>wen1){
                wen1=i;
            }
            if(cha!=1000000000 && cha*(i-shu1)+a[shu1]<=0){
                wei1=i+1;
                ans++;
                flag=0;
                cha=1000000000;
                i--;
            }
        }
        else{
            flag++;
            if(flag==1){
                shu1=i;
            }
            else if(flag==2){
                if((a[i]-a[shu1])%(i-shu1)!=0){
                    wei1=i+1;
                    ans++;
                    flag=0;
                    cha=1000000000;
                    i--;
                }
                else{
                    cha=(a[i]-a[shu1])/(i-shu1);
                    if(wen1>=wei1){
                        if(a[i]-(i-wen1)*cha<=0){
                            wei1=i+1;
                            ans++;
                            flag=0;
                            cha=1000000000;
                            i--;
                        }
                    }
                }
            }
            else if(flag>2){
                if(a[i]!=cha*(i-shu1)+a[shu1]){
                    wei1=i+1;
                    ans++;
                    flag=0;
                    cha=1000000000;
                    i--;
                }
            }
        }
    }
    printf("%I64d\n",ans+1);
    return 0;
}