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.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.util.*;


public class Main {
	public static void main(String[] args) throws Exception {
		Main mainClass = new Main();
	}

	BufferedReader in;
	PrintWriter out;
	StringTokenizer st;

	public String next() throws Exception {
		if (st == null || !st.hasMoreTokens()) {
			st = new StringTokenizer(in.readLine());
		}
		return st.nextToken();
	}

	public int nextInt() throws Exception {
		return Integer.parseInt(next());
	}



	public double nextDouble() throws Exception {
		return Double.parseDouble(next());
	}

	public long nextLong() throws Exception {
		return Long.parseLong(next());
	}

	public Main() throws Exception {
		in = new BufferedReader(new InputStreamReader(System.in));
		out = new PrintWriter(new OutputStreamWriter(System.out));

		solve();
		out.close();
	}

	public class IntMultiSet {
		TreeMap<Integer, Integer> t;
		// TODO;
	}

	int n, a[], lenNonNull[], lastNonNull[], len[], diff[], ans[];
	IntMultiSet w;

	public final static int ANY = Integer.MIN_VALUE;

	public void solve() throws Exception {
		int n = nextInt();
		a = new int [n];
		len = new int [n];
		lenNonNull = new int [n];
		diff = new int [n];
		lastNonNull = new int[n];
		ans = new int [n];

		int lastNonNullIdx = -1;
		for (int i= 0 ; i < n ; i++) {
			a[i] = nextInt();
			lastNonNull[i] = lastNonNullIdx;
			if (a[i] > -1) {
				lastNonNullIdx = i;
			} 
			
		}

		for (int i = 0 ; i < n ; i ++) {
			if (a[i] == -1) {
				continue;
			} else {
				lastNonNullIdx = lastNonNull[i];
				if (lastNonNullIdx == -1) {
					lenNonNull[i] = 1;
					len[i] = i+1;
					diff[i] = ANY;
				} else {
					
					if (diff[lastNonNullIdx] == ANY) {
						
						int d = (a[i] - a[lastNonNullIdx]) / (i - lastNonNullIdx);
						if ( (a[i] - a[lastNonNullIdx]) % (i - lastNonNullIdx) == 0) {
							lenNonNull[i] = lenNonNull[lastNonNullIdx] + 1;
							len[i] = len[lastNonNullIdx] + (i - lastNonNullIdx);	
							diff[i] = d;
						} else {
							lenNonNull[i] = 1;
							len[i] = (i - lastNonNullIdx);	
							diff[i] = ANY;
						}
						


					} else {
						long projected = a[lastNonNullIdx] + 1L * (i - lastNonNullIdx) * diff[lastNonNullIdx];
						//out.println("proj " + a[i] + " " + projected);	
						int d = (a[i] - a[lastNonNullIdx]) / (i - lastNonNullIdx);
						if (projected == a[i]) {
							diff[i] = diff[lastNonNullIdx];
							lenNonNull[i] = lenNonNull[lastNonNullIdx] + 1;
							len[i] = len[lastNonNullIdx] + i - lastNonNullIdx;
						} else if ( (a[i] - a[lastNonNullIdx]) % (i - lastNonNullIdx) == 0) {
							lenNonNull[i] = 2;
							len[i] = (i - lastNonNull[lastNonNullIdx]);	
							diff[i] = d;
						} else {
							lenNonNull[i] = 1;
							len[i] = (i - lastNonNullIdx);	
							diff[i] = ANY;
						}
					}
					 
				}
			}
		}
/*
		for (int i = 0 ; i < n ; i ++) {
			out.println( a[i] + "\t" + lastNonNull[i] + "\t" + lenNonNull[i] + "\t" + len[i] + "\t" + diff[i]);
		}
*/		
		
		for (int i = 0 ; i < n ; i++) {
			if (a[i] == -1) {
				if (i == 0)
					ans[i] = 1;
				else 
					ans[i] = ans[i-1];
				//out.println(a[i] + ":\t" + ans[i]);
				continue;
			}


			int l = len[i];
			int prev = i - l;
			if (prev < 0) {
				ans[i] = 1;
			} else {
				ans[i] = ans[prev] + 1;
			}
			//out.println(a[i] + ":\t" + ans[i]);
		}
		out.println(ans[n-1]);

		



	}
}








