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

n=int(input())

A=list(map(int,input().split()))

P=[]

for i in range(n):
    if(A[i]!=-1):
        P.append((A[i],i))
if(len(P)==0 or len(P)==1):
    print(1)

else:
    p=10**10
    d=10**10
    z=10**10
    start=0
    for i in range(n):
        if(A[i]==-1):
            if(d==10**10):
                continue
            else:
                A[i]=A[i-1]+d
                if(A[i]<0):
                    A[i]=-1
                    d=10**10
                    start=i
        else:
            if(d==10**10):
                if(p==10**10):
                    p=A[i]
                    z=i
                else:
                    D=A[i]-p
                    if(D%(i-z)==0):
                        for k in range(i-1,z,-1):
                            A[k]=A[k+1]-(D//(i-z))
                        r=False
                        for k in range(z-1,start-1,-1):
                            if(r==False):
                                A[k]=A[k+1]-(D//(i-z))
                                if(A[k]<=0):
                                    A[k]=1
                                    r=True
                            else:
                                A[k]=1
                        d=D//(i-z)
                    else:
                        for k in range(start,i):
                            A[k]=p
                        start=i
                        d=10**10
                        p=A[i]
                        z=i
            else:
                x=A[i]-A[i-1]
                if(x==d):
                    continue
                else:
                    z=i
                    start=i
                    p=A[i]
                    d=10**10
    if(A[-1]==-1):
        for k in range(start,n):
            A[k]=10
    d=A[1]-A[0]
    ans=1
    i=2
    while(i<n):
        if(A[i]-A[i-1]==d):
            i+=1
            continue
        else:
            ans+=1
            if(i==n-1):
                break
            i+=1
            d=A[i]-A[i-1]
        i+=1
    print(ans)
