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.util.Arrays;
import java.util.Scanner;

/**
 * Class: QuestionX<br />
 * Date: 2014/04/06 23:38<br />
 * Description:<br />
 *
 * @author Laiping Zhou(sjtudesigner)
 */
public class QuestionXX {

    private static class Tri implements Comparable<Tri>
    {
        public int num, c, p;
        public Tri(int num, int c, int p)
        {
            this.num = num;
            this.c = c;
            this.p = p;
        }
        @Override
        public int compareTo(Tri o) {

            if (p < o.p) return -1;
            else if (p > o.p) return 1;
            else return 0;
        }
    }
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        int[] arr = new int[a];
        int[] arr_dist = new int[a];
        int length = 0;
        int dist = 1;
        for (int i = 0;i < a;i++)
        {
            int temp = sc.nextInt();
            if (temp == -1) { dist++; continue; }
            arr[length] = temp;
            arr_dist[length] = dist;
            dist = 1;
            length++;
        }
/*        for (int i = 0;i < length;i++)
            System.out.printf("%d ", arr_dist[i]);*/

        boolean OUT_STATE = true;
        long diff_up = 0;
        long diff_down = 0;
        int result = 0;

        for (int i = 0;i < length;i++)
        {
            if (OUT_STATE && i + 1 != length) { diff_up = (arr[i + 1] - arr[i]); diff_down = arr_dist[i + 1]; i++; OUT_STATE = false;}
            else if (OUT_STATE) { break; }
            else
            {
                if ((arr[i] - arr[i - 1]) * diff_down != arr_dist[i] * diff_up) { OUT_STATE = true; i--; result++; }
            }
        }
        result++;
        // if (result == 0) result = 1;
        System.out.println(result);
    }

}
