1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
#ifndef LOCAL
#pragma GCC optimize("O3")
#endif
#include <bits/stdc++.h>
using namespace std;
#define sim template < class c
#define ris return * this
#define mor > muu & operator << (
#define R22(r) sim > typename \
  enable_if<1 r sizeof dud<c>(0), muu&>::type operator<<(c g) {
sim > struct rge {c b, e; };
sim > rge<c> range(c h, c n) { return {h, n}; }
sim > auto dud(c * r) -> decltype(cerr << *r);
sim > char dud(...);
struct muu {
#ifdef LOCAL
stringstream a;
~muu() { cerr << a.str() << endl; }
R22(<) a << boolalpha << g; ris; }
R22(==) ris << range(begin(g), end(g)); }
sim, class b mor pair < b, c > r) { ris << "(" << r.first << ", " << r.second << ")"; }
sim mor rge<c> u) {
a << "[";
for (c i = u.b; i != u.e; ++i) 
  *this << ", " + 2 * (i == u.b) << *i;
 ris << "]";
 }
#else
sim mor const c&) { ris; }
#endif
muu & operator()() { ris; }
};
#define imie(r...) "[" #r ": " << (r) << "] "
#define debug (muu() << __FUNCTION__ << "#" << __LINE__ << ": ")

int MAX = 1000 * 1000 * 1000;

int check(vector<int> v, bool dir) {
	int res = 0;
	for (int i = 0; i + 1 < v.size(); i ++) {
		if (dir && v[i] >= v[i+1]) {
			v[i+1] = MAX;
			res ++;
		}
		if (!dir && v[i] <= v[i+1]) {
			v[i+1] = -MAX;
			res ++;
		}
		dir = !dir;
	}
	return res;
}

int main() {
	ios_base::sync_with_stdio(0);
	int n;
	cin >> n;
	vector<int> v;
	for (int i = 0; i < n; i++) {
		int x;
		cin >> x;
		v.push_back(x);
	}
	cout << min(check(v, true), check(v, false));
}