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
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
#include <climits>
#include <iostream>
#include <vector>

using namespace std;

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  int n;
  cin >> n;
  vector<int> v;
  for (int i = 0; i < n; i++) {
    int a;
    cin >> a;
    v.push_back(a);
  }

  int prev = v[0];
  int cur = prev;

  bool turn = true;

  int wyn1 = 0;

  for (int i = 1; i < n; i++) {
    cur = v[i];

    if (turn) {  // up
      if (cur > prev) {
        // ok
      } else {
        cur = INT_MAX;
        wyn1++;
      }
    } else {  // down
      if (prev > cur) {
        // ok
      } else {
        cur = INT_MIN;
        wyn1++;
      }
    }

    turn ^= true;
    prev = cur;
  }

  turn = false;

  int wyn2 = 0;
  prev = v[0];
  for (int i = 1; i < n; i++) {
    cur = v[i];

    if (turn) {  // up
      if (cur > prev) {
        // ok
      } else {
        cur = INT_MAX;
        wyn2++;
      }
    } else {  // down
      if (prev > cur) {
        // ok
      } else {
        cur = INT_MIN;
        wyn2++;
      }
    }

    turn ^= true;
    prev = cur;
  }

  cout << min(wyn1, wyn2) << "\n";

  return 0;
}