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 dbgs(x) cerr << (#x) << " --> " << (x) << ' '
#define dbg(x) cerr << (#x) << " --> " << (x) << endl

#define foreach(i,x) for(type(x)i=x.begin();i!=x.end();i++)
#define FOR(ii,aa,bb) for(int ii=aa;ii<=bb;ii++)
#define ROF(ii,aa,bb) for(int ii=aa;ii>=bb;ii--)

#define type(x) __typeof(x.begin())

#define orta (bas + son >> 1)
#define sag (k + k + 1)
#define sol (k + k)

#define pb push_back
#define mp make_pair

#define nd second
#define st first

#define endl '\n'

typedef pair < int ,int > pii;

typedef long long ll;

const long long linf = 1e18+5;
const int mod = (int) 1e9 + 7;
const int logN = 17;
const int inf = 1e9;
const int N = 2e5 + 5;

int next, n, m, x, y, a[N];

int main() {
	scanf("%d", &n);
	vector< pii > v;
	int ans = 0;
	v.pb(mp(0, 0));
	FOR(i, 1, n) {
		scanf("%d", &a[i]);
		if(a[i] > 0)
			v.pb(mp(a[i], i));
	}
	int s = v.size() - 1;
	FOR(i, 1, s) {
		int t = i;
		if(i == s)
			ans++;
		else {
			if(abs(v[i].st-v[i+1].st) % (v[i+1].nd - v[i].nd)) {
				ans++;
			}
			else {
				int diff = (v[i+1].st - v[i].st) / (v[i+1].nd - v[i].nd);
				while(i < s && v[i].st + diff * (v[i+1].nd - v[i].nd) == v[i+1].st)
					i++;
				ans++;
				if(next && v[t].st - next * diff <= 0) ans++;
				next = n+1;
				if(i != s)
				next = v[i+1].nd;
				next -= v[i].nd + 1;
				if(v[i].st + next * diff > 0) 
					next = 0;
			}
		}
	}
	if(next) ans++;
	cout << max(1, ans) << endl;
	return 0;
}
