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.FileNotFoundException;
import java.util.Scanner;

public class D {

    static int[] a;
    static int n;
    static int ans = 0;

    public static void main(String zargs[]) throws FileNotFoundException {

        Scanner scanner = new Scanner(System.in);

        n = scanner.nextInt();

        a = new int[n];

        for (int i = 0; i < n; i++) {
            a[i] = scanner.nextInt();
        }

        int i = 0;
        while (i < n && a[i] == -1)
            i++;

        check(i);
//        for (i = 0; i < n; i++)
//            System.out.println(a[i]);
        System.out.println(ans);
    }

    private static void check(int i) {
        ans++;
        int aa;
        if (i < n) {
            aa = a[i];
        } else return;

        Integer diff = null;

        int j = i + 1;
        for (; j < n; j++) {
            if (a[j] == -1) {
                if (diff == null) {
//                    continue;
                } else {
                    a[j] = aa + (j - i) * diff;
                }
            } else {
                if (diff != null) {
                    if (a[j] == aa + (j - i) * diff) {
//                        continue;
                    } else {
                        check(j);
                        return;
                    }
                } else {
                    if ((a[j] - aa) % (j - i) == 0) {
                        diff = (a[j] - aa) / (j - i);
                    } else {
                        check(j);
                        return;
                    }
                }
            }

        }
    }


}
