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 _ ios_base::sync_with_stdio(0);cin.tie(0);
#define endl '\n'
#define debug(x) cerr << #x << " == " << (x) << '\n';
#define all(X) begin(X), end(X)
#define size(X) (int)std::size(X)

using ll = long long;

const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;

int main()
{ _
    int n; cin >> n;

    vector<ll> a(n);
    for (auto& x : a) cin >> x;

    vector<pair<ll, int>> p;

    for (int i = 0; i < n; ++i)
    {
        if (a[i] != -1) p.emplace_back(a[i], i);
    }

    const int k = size(p);

    int ans = 1;
    ll d = 0;

    if (k >= 2)
    {
        d = (p[1].first - p[0].first) / (p[1].second - p[0].second);

        if (auto [a, x] = p[0]; a - d * x < 1) ans += 1;
    }

    for (int i = 1; i < k; ++i)
    {
        auto [aprev, xprev] = p[i - 1];
        auto [acur, xcur] = p[i];

        if ((xcur - xprev) * d + aprev != acur)
        {
            if (not (i == 1 && ans == 2)) ans += 1;

            if (i + 1 < k)
            {
                auto [anext, xnext] = p[i + 1];
                d = (anext - acur) / (xnext - xcur);
            }
        }
    }

    if (auto [a, x] = p[k - 1]; k > 1 && a + (n - x) * d < 1) ans += 1;

    cout << ans << endl;

    exit(0);
}
