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

// Don't place your source in a package

import java.math.BigInteger;
import java.util.*;
import java.lang.*;
import java.io.*;



// Please name your class Main
public class Main {
    static FastScanner fs=new FastScanner();
    static class FastScanner {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st=new StringTokenizer("");
        public String next() {
            while (!st.hasMoreElements())
                try {
                    st=new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            return st.nextToken();
        }
        int Int() {
            return Integer.parseInt(next());
        }

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

        String Str(){
            return next();
        }
    }


    public static void main (String[] args) throws java.lang.Exception {
        PrintWriter out = new PrintWriter(System.out);


        int T=1;
        for(int t=0;t<T;t++){
            int n=Int();
            int A[]=new int[n];
            for(int i=0;i<n;i++){
                A[i]=Int();
            }
            Solution sol=new Solution(out);
            sol.solution(A);
        }
        out.flush();

    }


    public static int Int(){
        return fs.Int();
    }
    public static long Long(){
        return fs.Long();
    }
    public static String Str(){
        return fs.Str();
    }

}






class Solution{
    PrintWriter out;
    public Solution(PrintWriter out){
        this.out=out;
    }




    public void solution(int A[]){
        int res=0;
        int n=A.length;

        boolean good=false;
        int pre=-1,pred=-1;

        for(int i=0;i<A.length;i++){
            //System.out.println(i);
            res++;
            int j=i;
            while(j<n&&A[j]==-1)j++;
            int k=j+1;
            while(k<n&&A[k]==-1)k++;
            if(k>=n)break;



            int cnt1=j-i;
            int d=(A[k]-A[j])/(k-j);
            //System.out.println(j+"  "+k+"  "+d+"   "+cnt1);
            //System.out.println();

            if((A[k]-A[j])%(k-j)!=0){
                i=k-1;
                continue;
            }


            if(A[j]-cnt1*d<=0){
                i=k-1;
                continue;
            }

            i=k+1;
            while(i<A.length&&((A[i]==-1&&A[k]+(i-k)*d>0)||A[i]==A[k]+(i-k)*d)){
                i++;
            }
            i--;
        }


        out.println(res);
    }














}



/*
                             ;\
                            |' \
         _                  ; : ;
        / `-.              /: : |
       |  ,-.`-.          ,': : |
       \  :  `. `.       ,'-. : |
        \ ;    ;  `-.__,'    `-.|
         \ ;   ;  :::  ,::'`:.  `.
          \ `-. :  `    :.    `.  \
           \   \    ,   ;   ,:    (\
            \   :., :.    ,'o)): ` `-.
           ,/,' ;' ,::"'`.`---'   `.  `-._
         ,/  :  ; '"      `;'          ,--`.
        ;/   :; ;             ,:'     (   ,:)
          ,.,:.    ; ,:.,  ,-._ `.     \""'/
          '::'     `:'`  ,'(  \`._____.-'"'
             ;,   ;  `.  `. `._`-.  \\
             ;:.  ;:       `-._`-.\  \`.
              '`:. :        |' `. `\  ) \
      -hrr-      ` ;:       |    `--\__,'
                   '`      ,'
                        ,-'


                      free bug dog
*/





