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 D {
	FastScanner in = new FastScanner(System.in);
	PrintWriter out = new PrintWriter(System.out);

	int INF = 1500000000;
	public void run() {
		int n = in.nextInt();
		int[] a = in.nextIntArray(n);
		
		long res = 1;
		
		boolean down = false;
		int mcnt = a[0] == -1 ? 1 : 0;
		long prev = INF;
		long d = INF;
		for (int i = 1; i < n; i++) {
//			System.out.println(i + " : " + prev + " " + d + " " + mcnt + " " + res);
			if (a[i] != -1) {
				if (a[i-1] == -1) {
					if (prev == INF) {
						if (a[i] - mcnt <= 0) {
							down = true;
						}
						mcnt = 0;
						continue;
					}
					
					if (d != INF) {
						if (prev + (mcnt + 1) * d != a[i]) {
							res++;
							d = INF;
						}
					} else {
						if (Math.abs(prev - a[i]) % (mcnt + 1) != 0) {
							res++;
						} else {
							d = (a[i] - prev) / (mcnt + 1);							
						}
					}
					mcnt = 0;
				} else {
					if (d == INF) {
						if (down) {
							if (a[i] - a[i-1] > 0) res++;
							down = false;
						}
						else d = a[i] - a[i-1];
					} else if (d != a[i] - a[i-1]) {
						res++;
						d = INF;
					}
				}
			} else {
				if (a[i-1] != -1) {
					prev = a[i-1];
				}
				mcnt++;
			}
		}
		if (prev + d * (mcnt + 1) <= 0) res++;
		System.out.println(res);
		/*
		int[] mcnt = new int[n];
		int[] dif = new int[n];
		int[] r = new int[n];
		int[] l = new int[n];
		
		int cur = 0;
		int d = INF;
		for (int i = 1; i < n; i++) {
			if (a[i] != -1) {
				if (a[i-1] == -1) {
					r[cur] = a[i];
					cur++;
				} else {
					int nd = a[i] - a[i-1];
					if (nd != d) {
						if (d != INF) res++;
						d = nd;
					}
					dif[cur] = d;
				}
			} else {
				mcnt[cur]++;
				if (a[i-1] != -1) {
					l[cur] = a[i-1];
				}
				d = INF;
			}
		}
		dif[cur+1] = d;
		mcnt = Arrays.copyOf(mcnt, cur);
		dif = Arrays.copyOf(dif, cur + 1);
		r = Arrays.copyOf(r, cur);
		l = Arrays.copyOf(l, cur);
		System.out.println(Arrays.toString(mcnt));
		System.out.println(Arrays.toString(dif));
		System.out.println(Arrays.toString(l));
		System.out.println(Arrays.toString(r));
		*/
		
		out.close();
	}

	public static void main(String[] args) {
		new D().run();
	}

	public void mapDebug(int[][] a) {
		System.out.println("--------map display---------");

		for (int i = 0; i < a.length; i++) {
			for (int j = 0; j < a[i].length; j++) {
				System.out.printf("%3d ", a[i][j]);
			}
			System.out.println();
		}

		System.out.println("----------------------------");
		System.out.println();
	}

	public void debug(Object... obj) {
		System.out.println(Arrays.deepToString(obj));
	}

	class FastScanner {
		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;

		public FastScanner(InputStream stream) {
			this.stream = stream;
			//stream = new FileInputStream(new File("dec.in"));

		}

		int read() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}

		boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		boolean isEndline(int c) {
			return c == '\n' || c == '\r' || c == -1;
		}

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

		int[] nextIntArray(int n) {
			int[] array = new int[n];
			for (int i = 0; i < n; i++)
				array[i] = nextInt();

			return array;
		}

		int[][] nextIntMap(int n, int m) {
			int[][] map = new int[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextIntArray(m);
			}
			return map;
		}

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

		long[] nextLongArray(int n) {
			long[] array = new long[n];
			for (int i = 0; i < n; i++)
				array[i] = nextLong();

			return array;
		}

		long[][] nextLongMap(int n, int m) {
			long[][] map = new long[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextLongArray(m);
			}
			return map;
		}

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

		double[] nextDoubleArray(int n) {
			double[] array = new double[n];
			for (int i = 0; i < n; i++)
				array[i] = nextDouble();

			return array;
		}

		double[][] nextDoubleMap(int n, int m) {
			double[][] map = new double[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextDoubleArray(m);
			}
			return map;
		}

		String next() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}

		String[] nextStringArray(int n) {
			String[] array = new String[n];
			for (int i = 0; i < n; i++)
				array[i] = next();

			return array;
		}

		String nextLine() {
			int c = read();
			while (isEndline(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isEndline(c));
			return res.toString();
		}
	}
}

