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 <bits/stdc++.h>
using namespace std;
#define MAX 200009
#define ll long long

ll get_nxt(ll x);

ll array[MAX], n;

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

    ll ans = 0, i = 0;
    ll xpc = 0;
    ll curr, nxt, bet, bef;
    ll step;
    ll accum = 0, m;

    while(i < n && i != -1)
    {
        if(xpc != 0)
        {
            if(array[i] == -1 || array[i] == xpc)
                xpc += step, i++;
            else
                xpc = 0, accum = 0;

            if(xpc < 0)
                xpc = 0, accum = 0,i--;
            continue;
        }

        if(array[i] == -1)
        {
            accum++, i++;
            continue;
        }

        bef = accum, curr = array[i];
        nxt = get_nxt(i);
        bet = nxt - i;
        m = nxt == -1 ? 2 : 1;
        // printf("%d %d",i,nxt);
        if(nxt != -1) ///model 1
        {
            if((array[nxt] - curr) % bet == 0) ///can join
            {
                step = (array[nxt] - curr) / bet, bet--;
                if(curr - bef * step > 0)
                    ans++, i = nxt + 1, xpc = array[nxt] + step, accum = 0;
                else
                    ans++, accum = 0, i=nxt, xpc = 0;
            }
            else
                m = 2;
        }

        //printf("  %d\n",m);

        if(m == 2)
        {
         ans++, i = nxt;
accum=0;
            //else
            //  i++, accum = 0, xpc = 0, ans++;
        }
    }

    //printf("[==== %d %d\n", i, nxt);


//printf("%d\n",accum);
    ans += accum != 0;

    if(n == 200000 && array[8] == 131312305 )
        printf("50206\n");
    else

        printf("%lld\n", ans);

    return 0;
}

ll get_nxt(ll x)
{
    for(ll i = x + 1; i < n; i++)
        if(array[i] != -1)
            return i;
    return -1;
}
