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.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;

public class Task {
       static BufferedReader br ;
       static PrintWriter out;
       
       static boolean isSpace(int ch){
    	   return ((ch==10||ch==32)||(ch==9||ch==13));
       }
       
       static int readInt() throws IOException{
           int ret = 0,sign=1;
           int ch = br.read();
           while(isSpace(ch))ch=br.read();
           if(ch==45){sign*=-1;ch=br.read();}
           do{
               ret*=10;
               ret+=(ch-48);
               ch = br.read();
           }while(48<=ch&&ch<=57);
           return sign*ret;
       }
       
       static String readString() throws IOException{
    	   StringBuffer sb = new StringBuffer();
    	   int ch = br.read();
    	   while(isSpace(ch))ch=br.read();
    	   do{
    		   sb.append((char) ch);
    		   ch = br.read();
    	   }while(!isSpace(ch));
    	   return sb.toString();
       }
       
       public static void main(String[] args)throws IOException{
    	   br = new BufferedReader(new InputStreamReader(System.in));
    	   out = new PrintWriter(System.out);
    	   int n = readInt();
    	   int[] a = new int[n+1];
    	   for(int i=1;i<=n;i++)a[i]=readInt();
    	   int[] diff = new int[n+1];
    	   for(int j=1;j<=n;j++){
    		   diff[j]=(a[j]!=-1)?a[j]-a[j-1]:1000000001;
    	   }
    	   int curdiff = diff[1];
    	   int num_ap=0;
    	   for(int i=2;i<=n;i++){
    		   if(diff[i]==curdiff)continue;
    		   else if(diff[i]==1000000001)diff[i]=curdiff;
    		   else {
    			    ++num_ap;
    			    curdiff = (i+1<=n)?diff[i+1]:0;
    		   }
    	   }
    	   if(num_ap==0)++num_ap;
    	   out.println(num_ap);
    	   out.close();
       }
}