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
#include <iostream>
#include <vector>

using namespace std;

int MAX_V = 1000000000;
int MIN_V = -MAX_V;

int solve(vector<int> &vec) {
    int cnt_a = 0, cnt_b = 0;
    int last_a = vec[0], last_b = vec[0];

    for(int i = 1; i < vec.size(); i++) {
        if(i & 1) {
            if(last_a > vec[i]) {
                last_a = vec[i];
            } else {
                last_a = MIN_V;
                cnt_a++;
            }
            if(last_b < vec[i]) {
                last_b = vec[i];
            } else {
                last_b = MAX_V;
                cnt_b++;
            }
        } else {
            if(last_a < vec[i]) {
                last_a = vec[i];
            } else {
                last_a = MAX_V;
                cnt_a++;
            }
            if(last_b > vec[i]) {
                last_b = vec[i];
            } else {
                last_b = MIN_V;
                cnt_b++;
            }
        }
    }

    return cnt_a < cnt_b ? cnt_a : cnt_b;
}

int main() {
    ios_base::sync_with_stdio(false);
    int n;
    cin >> n;
    vector <int> vec;
    for(int i = 0; i < n; i++) {
        int x;
        cin >> x;
        vec.push_back(x);
    }

    cout << solve(vec) << endl;
    return 0;
}