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 <fstream>

#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <string>

using namespace std;

#define int long long int
vector <int> a;
int i,j,n,k;
int endat,startat;
int start;
int f,s,d;
bool def;
int ans = 0;


void find(int v) {
    f = v;
    while ((f < n)&&(a[f] == -1)) {
        ++f;
    }
    s = f + 1;
    while ((s < n)&&(a[s] == -1)) {
        ++s;
    }
}

bool bnd(int v) {
    return ((0<=v)&&(v<n));
}
void main() {

    cin >> n;
    a.resize(n);

    for (i = 0; i < n; ++i) {
        cin >> a[i];
    }

    ans = 0;
    start = -1;
    find(0);
    if (bnd(s)&&bnd(f)) {
        if ((a[s] - a[f])%(s - f) == 0) {
            d = (a[s] - a[f])/(s - f);
            if (a[f] - d*f <= 0) {
                ++ans;
            }
        }
    }
    d = 0;
    def = false;
    endat = n;
    startat = -1;
    while (s < n) {
        if (!def) {
            if ((a[s] - a[f])%(s - f) == 0) {
                d = (a[s] - a[f])/(s - f);
                start = f;
                if (d>0) {
                    startat =s - a[s] / d;
                    if (a[s]%d == 0) ++startat;
                    if (startat - endat>1) ++ans;
                }
                if (d<0) {
                    endat = a[s] / (-d) + s;
                    if (a[s]%d == 0) --endat;
                }
                def = true;
            } else {
                ++ans;
                def = false;
            }
        } else {
            if (((a[s] - a[f])%(s - f) == 0)&&((a[s] - a[f])/(s - f) == d)) {
                d = (a[s] - a[f])/(s - f);
                def = true;
            } else {
                ++ans;
                def = false;
            }
        }
        ++f;
        while ((f < n)&&(a[f] == -1)) {
            ++f;
        }
        find(f);
    }
    
    if ((def)&&(start!=-1))
    if (a[start] + d*((n-1) - start) <= 0) ++ans;

    cout << ans + 1;
    return;
}