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 <string.h>
__int64 a[222222];
int main()
{
	int n;
	while(~scanf("%d",&n))
	{
		memset(a,0,sizeof(a));
		int sum =1;
		__int64 p;
		__int64 q;
		int i,j,k;
		int b=0;  
		int time ;
		__int64 d =0 ;
		for (i=0;i<n;i++)
		{
			scanf("%I64d",&a[i]);
		}
		for(i=b;i<n;i++)
		{
			if(i==n-1)
			{
				break;
			}
			if(a[i] != -1)
			{
				time = 1;
				p=a[i];
				for(j=i+1;j<n;j++)
				{
					if(a[j] == -1)
						time++;
					else 
					{
						q=a[j];
						break;
					}
				}

				if((q-p) % time == 0)
				{

					d= (q-p)/time;
					for(k=j-1;k>=b;k--)
					{
						if(a[k] == -1)
						{
							if(a[k+1] -d > 0)
								a[k] = a[k+1] - d;
							else
							{
								b=k;
								i=b;
								break;
							}
						}

					}
					for (k=i+1;k<n;k++)
					{
						if (a[k]==-1)
						{
							if (a[k-1] + d <=0)
							{

							    b=k;
								i =b ;
								sum++;
								break;
							}
							else 
								a[k] = a[k-1] +d;
						}
						else 
						{
							if (a[k]!= a[k-1] + d)
							{
								/*
								printf("b=%d\n",b);
								printf("xulie:");
								for (int m=b ;m<k;m++)
									printf("%I64d ",a[m]);
								printf("\n");
								printf("sum=%d\n",sum);
								printf("\n");
								*/

								
							    b=k;
								i = b;
								sum++;
								break;
							}
						}
					}

				}
			}
		}
	/*	for(i=0;i<n;i++)
		{
			printf("%I64d ",a[i]);
		}*/
		printf("%d\n",sum);
	}
	return 0;
}

	 		    			 	  		 	 	 		 	  		