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.Scanner;

public class PopulationSizeSolver {

    private int n;
    private int[] a;


    private int start;
    private int prev;
    private int difference;

    public static void main(String[] args) {
        PopulationSizeSolver solver = new PopulationSizeSolver();

        solver.readData();
        int solution = solver.solve();
        solver.print(solution);
    }

    private void print(int value) {
        System.out.println(value);
    }

    private void readData() {
        Scanner scanner = new Scanner(System.in);

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

    private int solve() {
        int result = 1;

        start = 0;
        prev = a[start] > 0 ? start : -1;
        difference = Integer.MAX_VALUE;
        for (int i = 1; i < n; i++) {
            if (a[i] > 0) {
                if (difference != Integer.MAX_VALUE) {
                    if (!(((a[prev] + (i - prev) * difference) == a[i]) && (a[i] - (i - start) * difference > 0))) {
                        result++;
                        start = i;
                        prev = i;
                        difference = Integer.MAX_VALUE;
                    }
                } else {
                    if (prev >= 0) {
                        int rem = (a[i] - a[prev]) % (i - prev);
                        int diff = (a[i] - a[prev]) / (i - prev);
                        if (rem == 0 && (a[i] - (i - start) * diff) > 0) {
                            difference = diff;
                        } else {
                            result++;
                            start = i;
                            prev = i;
                            difference = Integer.MAX_VALUE;
                        }
                    } else {
                        prev = i;
                    }
                }
            } else {
                if (difference != Integer.MAX_VALUE) {
                    if ((a[start] + (i - start) * difference) <= 0) {
                        result++;
                        start = i;
                        prev = -1;
                        difference = Integer.MAX_VALUE;
                    }
                }
            }
        }


        return result;
    }
}
