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.math.BigInteger;
import java.util.*;
import java.util.Map.Entry;

import static java.lang.Math.*;
 
public class solver implements Runnable {
        final boolean ONLINE_JUDGE = System.getProperty("ONLINE_JUDGE") != null;
        BufferedReader in;
        PrintWriter out;
        StringTokenizer tok = new StringTokenizer("");
        
        String readString() throws IOException{
                while(!tok.hasMoreTokens()){
                        try{
                                tok = new StringTokenizer(in.readLine());
                        }catch (Exception e){
                                return null;
                        }
                }
                return tok.nextToken();
        }
        String readString(String delim) throws IOException{
            while(!tok.hasMoreTokens()){
                    try{
                            tok = new StringTokenizer(in.readLine());
                    }catch (Exception e){
                            return null;
                    }
            }
            return tok.nextToken(delim);
    }
       
        int readInt() throws IOException{
                return Integer.parseInt(readString());
        }  
        long readLong() throws IOException{
                return Long.parseLong(readString());
        }      
        double readDouble() throws IOException{
                return Double.parseDouble(readString());
        } 
        char readChar() throws IOException {
            char val = 0;
            do{
                val = (char) in.read();
            }while(val == '\n' || val == '\r');
            return val;
        }
        char readChar(String skipChars)throws IOException{
            char val = 0;
            boolean ret;
            do{
                val = (char) in.read();
                ret = false;
                for (int i = skipChars.length()-1; i >= 0; i--){
                    if (skipChars.charAt(i) == val){
                        ret = true;
                        break;
                    }
                }
            }while(ret);
            return val;
        }
        
        void readIntArray(int[] arr, int start, int count) throws IOException{
            for (int i = 0; i < count; i++){
                arr[i+start] = readInt();
            }
        }
        
        public class Pair<T1,T2> {
            public T1 x1;
            public T2 x2;
            public Pair(){};
            public Pair(T1 x1, T2 x2){
                this.x1 = x1;
                this.x2 = x2;
            }
            public String toString(){
                return x1.toString() + " " + x2.toString();
            }
        }
        public class Point implements Comparable<Point>{
            public int x1, x2;
            public Point(){}
            public Point(int a, int b){x1 = a;x2=b;}
            public int compareTo(Point o) {
                return (x1-o.x1);
            }
            public String toString(){
                return x1 + ":" + x2;
            }
        }
        public class Tree implements Comparable<Tree>{
            public int x1, x2, x3;
            public Tree(){}
            public Tree(int a, int b, int c){x1 = a;x2=b;x3=c;}
            public int compareTo(Tree o) {
                if (x2 == o.x2) return (o.x1 - x1);
                return -(x2-o.x2);
            }
            public String toString(){
                return x1 + ":" + x2  + ":" +x3;
            }
        }
//----------------------------------------        
        
        
        public void solve() throws IOException {
            int n = readInt();
            int[] a = new int[n];
            boolean first = !false;
            boolean second = !false;
            boolean[] used = new boolean[n];
            int start = -1;
            int start2 = -1;
            for (int i =0 ; i < n; i++){
                a[i] = readInt();
                if (a[i] != -1 && first){
                    start = i;
                    first = false;
                    continue;
                }
            }
            
            if (start == -1){
                out.print(1);
                return;
            }
            
            
            int li = -1;
            int lli = -1;
            int ld = -1;
            int ans = 1;
            
            
            for (int i = 0; i < n; i++){
                if (a[i] == -1){
                    if (li == -1){
                        li = i;
                    }
                }else{
                    if (li == -1){
                        li = i;
                    }
                    if (lli == -1){
                        lli = i;
                        continue;
                    }
                    if (ld == -1){
                        if ((long)(a[i] - a[lli]) != (long)((a[i] - a[lli])/(i - lli))*(i - lli)){
                            ld = 1;
                            if (a[lli] + 1*(li - lli) > 0 || a[lli] - 1*(li - lli) > 0){
                                ans++;
                            }else{
                                ans+=2;
                            }
                            lli = i;
                            ld = -1;
                            li = i;
                        }
                        else{
                            ld = (a[i] - a[lli])/(i - lli);
                        }
                    }else{
                        if (a[i] != a[lli] + ld*(i - lli)){
                            if (a[li] == a[lli] + ld*(li - lli) || (a[li] == -1 && a[lli] + ld*(li - lli) > 0)){
                                ans++;
                            }else{
                                ans+=2;
                            }
                            lli = i;
                            ld = -1;
                            li = i;
                        }
                    }
                }
                
            }
            out.print(ans);
            
        }
        
        
//----------------------------------------
        public static void main(String[] args){
                new Thread(null, new solver(), "", 256 * (1L << 20)).start();
        }
       
        public void run(){
                try{
                        timeBegin = System.currentTimeMillis();
                        
                        if (ONLINE_JUDGE){
                            in = new BufferedReader(new InputStreamReader(System.in));
                            out = new PrintWriter(System.out);
                        } 
                        else {
                            in = new BufferedReader(new FileReader("input.txt"));
                            out = new PrintWriter("output.txt");
                        }
                        
                        solve();
                        out.close();
                        
                        timeEnd = System.currentTimeMillis();
                        System.err.println("Time = " + (timeEnd - timeBegin));
                }catch (Exception e){
                        e.printStackTrace(System.err);
                        System.exit(-1);
                }
        }
       
        long timeBegin, timeEnd;
 
        
//-------ДЕРЕВО ОТРЕЗКОВ       
        int[] doo;
        
        void update(int v, int i, int val, int ll, int rr){
            if (ll == rr){
                doo[v] = val;
            }else{
                int med = ll + (rr-ll)/2;
                
                if (i <= med){
                    update(2*v, i, val, ll, med);
                }else{
                    update(2*v+1, i, val, med+1, rr);
                }
                doo[v] = max(doo[2*v],doo[2*v+1]);
            }
        }
        int get(int v, int l, int r, int ll, int rr){
            if (l > r){
                return 0;
            }
            if (ll == l && r == rr){
                return doo[v];
            }
            int med = ll +(rr-ll)/2;
            return max(get(2*v, l, min(r, med), ll, med), 
                    get(2*v+1, max(l, med+1), r, med+1, rr));
        }
 //----------------------------------------         
}