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.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;


public class D {

	static BufferedReader br;
	static PrintWriter out;
	static StringTokenizer tokenizer;
	public static void main(String[] args) throws IOException {
		br = new BufferedReader(new InputStreamReader(System.in));
		out = new PrintWriter(System.out);
		
		tokenizer = new StringTokenizer(br.readLine());
		int n = Integer.parseInt(tokenizer.nextToken());
		
		long[] a = new long[n];
		tokenizer = new StringTokenizer(br.readLine());
		for(int i=0;i<n;i++){
			a[i] = Long.parseLong(tokenizer.nextToken());
		}
		
		long[]cnt = new long[n];
		long[]step = new long[n];
		long[] currentNum = new long[n];
		cnt[0] = 1;
		step[0] = -1;
		for(int i=0;i<n;i++){
			step[i] = -1000100000;
			currentNum[i] = -1;
		}
		long left=-1;
		long right=-1;
		int distance = -1;
		for(int i=0;i<n;i++){
			if(a[i]!=-1){
				currentNum[i] = a[i];
			}
			if(i>0){
				cnt[i] = cnt[i-1];
				step[i] = step[i-1];
			}
			if(a[i]!=-1){
				if(left==-1){
					left = a[i];
					distance = 0;
					step[i] = -1000100000;
				}else{
					if(right==-1){
						right = a[i];
						if((right-left)%distance!=0){
							cnt[i]++;
							left = right;
							right = -1;
							distance = 0;
							step[i] = -1000100000;
						}else{
							step[i] = (right-left)/distance;
							int j = i-1;
							while(j>=0 && cnt[j]==cnt[i]){
								if(a[j]==-1){
									long current = right-step[i]*(i-j);
									if(current<=0 /*|| current>1000000000*/){
										for(int z=j+1;z<=i;z++){
											cnt[z]++;	
										}
									}else{
										currentNum[j] = current;
										step[j] = step[i];
									}
									
								}
								j--;
							}
						}
					}else{
						long current = left+step[i]*distance;
						if(current!=a[i]){
							cnt[i]++;
							step[i] = -1000100000;
							left = a[i];
							right = -1;
							distance = 0;
						}
					}
				}
			}else{
				if(step[i]!=-1 && right!=-1){
					long current = left+step[i]*distance;
					if(current<=0 /*|| current>1000000000*/){
						cnt[i]++;
						step[i] = -1000100000;
						left = -1;
						right = -1;
						distance = 0;
					}else{
						currentNum[i] = current;
					}
				}
			}
			
			distance++;
		}
		
		long res = cnt[n-1];
		/*
5
-1 -1 -1 2 4
		 */
		/*long currentStep = -1;
		long currentNum = -1;
		for(int i=n-1;i>=0;i--){
			if(i==n-1){		
				currentStep = step[i];
			}else{
				if(cnt[i]!=cnt[i+1])if(step[i]!=-1000100000){
					currentStep = step[i];
			}
		}*/
		
		out.append(""+res);
		/*out.append("\n");
		for(int i=0;i<n;i++){
			out.append(cnt[i]+"\t");
		}
		
		out.append("\n");
		for(int i=0;i<n;i++){
			out.append(step[i]+"\t");
		}
		out.append("\n");
		for(int i=0;i<n;i++){
			out.append(currentNum[i]+"\t");
		}*/
		out.flush();
		out.close();

	}

}
