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


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class D {

    
    
    static StringBuilder sb=new StringBuilder();
    static void parse(String l, int[] here) {
        sb.setLength(0);
        int len=l.length(), j=0;
        for (int i=0; i<len; i++) {
            char c=l.charAt(i);
            if(c==' ') {
                here[j++]=Integer.parseInt(sb.toString());
                sb.setLength(0);
            } else {
                sb.append(c);
            }
        }
        if(sb.length()>0) {
            here[j++]=Integer.parseInt(sb.toString());
        }
    }
    
    static void run_stream(InputStream ins) throws IOException {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        int n=Integer.parseInt(br.readLine());
        
        int[] a=new int[n];
        parse(br.readLine(), a);
        
        
        int ret=1, l=0, ldef=a[0]>0? 0: -1, rat=Integer.MAX_VALUE;
        
        for (int i=1; i<n; i++) {
            if(a[i]>0) {
                if(rat!=Integer.MAX_VALUE) {
                    //in progress, lv must point to good index
                    if(a[ldef]+rat*(i-ldef)==a[i]) {
                        //good
                    } else {
                        ret++;
                        rat=Integer.MAX_VALUE;
                        l=ldef=i;
                    }
                } else {
                    if(ldef>=0) {
                        if((a[i]-a[ldef])%(i-ldef)==0) {
                            rat=(a[i]-a[ldef])/(i-ldef);
                            int v=a[ldef]-rat*(ldef-l);
                            if(v<0) {
                                ret++;
                                l=ldef;
                            }
                        } else {
                            ret++;
                            rat=Integer.MAX_VALUE;
                            l=ldef=i;
                        }
                    } else {
                        ldef=i;
                    }
                }
            } else {
                if(rat!=Integer.MAX_VALUE) {
                    int v=a[ldef]+rat*(i-ldef);
                    if(v<0) {
                        ret++;
                        l=i; ldef=-1;
                    }
                }
            }
        }
        
        System.out.println(ret);
    }

    public static void main(String[] args) throws IOException {
        run_stream(System.in);
    }

}
