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

#include<stdio.h>
#include<cstring>
#include<conio.h>
#include<algorithm>
using namespace std;
int i,j,n,dp[2][200005],r[200005],last,a[200005];

int main(void) {
   // freopen("file.in","r",stdin);
    
     scanf("%d",&n);
     
     for (i=1; i<=n; ++i) scanf("%d",&a[i]);
     
     dp[0][n]=1;
     dp[1][n]=1;
     if (a[n]==-1) last=n+1; else last=n;
     
     for (i=n-1; i>=1; --i) 
      if (a[i]!=-1) {
                    
                    int lung=last-i;
                    
                    dp[1][i]=min(dp[1][last],dp[0][last])+1;
                    
                    if ( (a[i]-a[last])%lung==0 ) {
                         
                         r[i]=(a[i]-a[last])/lung;
                         
                         if (r[i]==r[last]||last==n) dp[0][i]=dp[0][last];
                         else if (r[i]!=r[last]) dp[0][i]=min(dp[1][i],min(dp[1][last+1],dp[0][last+1])+1);
                         else dp[0][i]=dp[1][i];
                         
                         }
                    else dp[0][i]=dp[1][i];
                         
                    last=i;
                    
                    }   
      else {
           
           if (a[last]-(last-i)*r[last]>0) { dp[0][i]=dp[0][last]; dp[1][i]=dp[1][last]; }
           else { dp[0][i]=1+min(dp[0][last],dp[1][last]); dp[1][i]=dp[0][i]; }
           
           }
                    
     for (i=1; i<=n; ++i)
      if (a[i]!=-1) {
                    
                    int v1,v2;
                    
                    if (r[i]!=0) {
                                 
                                 if (a[i]-r[i]*i>0) v1=dp[0][i]; else v1=dp[0][i]+1;
                                 
                                 }
                    else v1=dp[0][i];
                                 
                    printf("%d",min(v1,dp[1][i]));
                    //getch();
                    return 0;
                    
                    
                    }
     printf("1"); 
     
    // getch();
    
    return 0;
}
