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>

using namespace std;

int count = 0;
int len = 0;
int num1 = 0;
int idx1 = -1;
int idx2 = -1;
int d = 0;

void reset(int input, int i) {
    ++count;
    num1 = input;
    idx1 = i;
    idx2 = -1;
    len = 1;
    d = 0;
}


int main(void) {
    int n;
    cin >> n;
    int input;
    for (int i = 0; i < n; ++i) {
        cin >> input;
        if (input == -1) {
            if (idx1 == -1 || idx2 == -1) {
                ++len;
            } else {
                long long cur = num1 + (long long)d * (i - idx1);
                if (cur >= 1) {
                    ++len;
                } else {
                    reset(input, -1);
                }
            }
        } else if (idx1 == -1) {
            ++len;
            num1 = input;
            idx1 = i;
        } else if (idx2 == -1) {
            if ((input - num1) % (i - idx1) == 0) {
                d = (input - num1) / (i - idx1);
                long long tmp = input - d * len;
                if (tmp >= 1) {
                    idx2 = i;
                    ++len;
                } else {
                    reset(input, i);
                }
            } else {
                reset(input, i);
            }
        } else {
            if (input == num1 + (long long)d * (i - idx1)) {
                ++len;
            } else {
                reset(input, i);
            }
        }
    }
    cout << count + 1 << endl;
    return 0;
}
