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.*;
import java.util.*;

public class PrD {
	public static void main(String[] args) throws IOException {
		new PrD().run();
	}

	BufferedReader in;
	PrintWriter out;
	StringTokenizer st;

	String nextToken() throws IOException {
		while (st == null || !st.hasMoreTokens()) {
			st = new StringTokenizer(in.readLine());
		}
		return st.nextToken();
	}

	int nextInt() throws IOException {
		return Integer.parseInt(nextToken());
	}

	void run() throws IOException {
		in = new BufferedReader(new InputStreamReader(System.in));
		out = new PrintWriter(System.out, true);
		solve();
		out.flush();
	}

	void solve() throws IOException {
		int n = nextInt();
		long[] a = new long[n];
		ArrayList<Integer> per = new ArrayList<Integer>();
		for (int i = 0; i < n; i++) {
			a[i] = nextInt();
			if (a[i] != -1) {
				per.add(i);
			}
		}
		if (per.size() == 0) {
			out.println(1);
			return;
		}
		if (per.size() == 1) {
			if (a[per.get(0)] > per.get(0) || a[per.get(0)] >= n - per.get(0)) {
				out.println(1);
				return;
			}
			out.println(2);
			return;
		}
		int cnt = 1;
		int last = 0;
		int p1 = 0;
		int p2 = 1;
		int sch = 2;
		int i = 0;
		while (i < n) {
			if (Math.abs(a[per.get(p2)] - a[per.get(p1)])
					% (per.get(p2) - per.get(p1)) != 0) {
				cnt++;
				if (sch == per.size()) {
					i = n;
					if (!(a[per.get(p2)] > per.get(p2) - per.get(p1) + 1 || a[per
							.get(p2)] >= n - per.get(p2))) {
						cnt++;
					}
				} else {
					last = (int) Math.min(per.get(p1) + a[per.get(p1)],
							per.get(p2));
					p1 = p2;
					p2 = sch;
					sch++;
				}
			} else {
				long con = (a[per.get(p2)] - a[per.get(p1)])
						/ (per.get(p2) - per.get(p1));
				if (a[per.get(p1)] - con * (per.get(p1) - last) <= 0) {
					cnt++;
				}
				i = per.get(p2) + 1;
				while (i < n
						&& ((a[i] == -1 && (i - per.get(p2)) * con > 0) || (a[i]
								- a[i - 1] == con))) {
					if (a[i] != -1) {
						sch++;
					}
					a[i] = (i - per.get(p2)) * con + a[per.get(p2)];
					i++;
				}
				if (i < n)
					cnt++;
				last = i;
				if (sch == per.size()) {
					i = n;
				} else {
					p1 = sch;
					sch++;
					if (sch == per.size()) {
						i = n;
						if (!(a[per.get(p1)] > per.get(p1) - last || a[per
								.get(p1)] >= n - per.get(p1))) {
							cnt++;
						}
					} else {
						p2 = sch;
						sch++;
					}

				}
			}
		}
		out.println(cnt);
	}
}
