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 <iostream>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <cstring>
using namespace std;
#define ll long long
#define MAX 200009

int fn();

int array[MAX], accum[MAX], n;

int main()
{
    scanf("%d", &n);
    for(int i = 0; i < n; i++)
        scanf("%d", &array[i]);

    printf("%d\n", fn());

    return 0;
}

int fn()
{
    memset(accum, -1, sizeof(accum));

    int lasti = -1, ret = 0, last;
    for(int i = n - 1; i >= 0; i--)
        if(array[i] != -1)
        {
            lasti = i;
            break;
        }

    if(lasti == -1)
        return 1;

    last = lasti;
    for(int i = last; i >= 0; i--)
    {
        accum[i] = last;
        if(array[i] != -1)
            last = i;
    }

    int i = 0, prog, first_i, sec_i, first, sec, b_first, b_sec, prog_i;

    last = prog = -99999999;

    while(i < n)
    {
        ///go ahead
        if(i > 0 && ((array[i] != -1 && last + prog == array[i]) || (array[i] == -1 && last + prog > 0)))
            last += prog, i++;
        else
        {
            if(accum[i]==-1)
            {
                ret++;
                break;
            }
            ///make new_sequence
            if(array[i] == -1)
                first_i = accum[i], sec_i = accum[first_i];
            else
                first_i = i, sec_i = accum[first_i];

            first = array[first_i], sec = array[sec_i];
            b_first = first_i - i, b_sec = sec_i - first_i;
            prog_i = sec_i - first_i;
            prog = sec - first;
            if(prog_i)
                prog = prog / prog_i;

            // printf("%d %d\n", i, prog);
            if(first + prog_i * prog == sec && first - b_first * prog > 0)
                ret++, last = sec, i = sec_i + 1;
            else
                ret++, i = sec_i;
        }
    }


    return ret;
}
