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
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
// while (clock()<=69*CLOCKS_PER_SEC)
// #pragma comment(linker, "/stack:200000000")
// #pragma GCC optimize("O3")
// #pragma GCC target ("avx2")
// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC optimize("unroll-loops")

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;

template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#define sim template <class c
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                    \
    sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(c i) \
    {
sim > struct rge {
    c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef XOX
    ~debug()
    {
        cerr << endl;
    }
    eni(!=) cerr << boolalpha << i;
    ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d)
{
    ris << "" << d.first << " --> " << d.second << "";
}
sim dor(rge<c> d)
{
    *this << "[";
    for (auto it = d.b; it != d.e; ++it)
        *this << ", " + 2 * (it == d.b) << *it;
    ris << "]";
}
#else
    sim dor(const c &)
    {
        ris;
    }
#endif
}
;
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "

#ifdef XOX
#warning Times may differ!!!
#endif

#define endl '\n'
#define pb emplace_back
#define vt vector
#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

const int nax = 1e6, mod = 1e9 + 7;

// #define int long long
void ckmin(int &a, int b)
{
    a = min(a, b);
}

int32_t main()
{
    cin.tie(0)->sync_with_stdio(0);
    int n;
    cin >> n;
    vt<int> v(n + 1);
    for (int i = 1; i <= n; i++) {
        cin >> v[i];
    }
    int ans = n;
    for (int parity : {0, 1}) {
        vt<vt<int>> dp(n + 1, vt<int>(3));
        dp[1][0] = 0;
        dp[1][1] = dp[1][2] = 1;
        for (int i = 2; i <= n; i++) {
            if (i % 2 == parity) {
                dp[i][0] = dp[i - 1][2];
                if (v[i - 1] > v[i]) {
                    ckmin(dp[i][0], dp[i - 1][0]);
                }
                dp[i][1] = min(dp[i - 1][0], dp[i - 1][2]) + 1;
                dp[i][2] = n;
            }
            else {
                dp[i][0] = dp[i - 1][1];
                if (v[i - 1] < v[i]) {
                    ckmin(dp[i][0], dp[i - 1][0]);
                }
                dp[i][1] = n;
                dp[i][2] = min(dp[i - 1][0], dp[i - 1][1]) + 1;
            }
        }
        ans = min({ans, dp[n][0], dp[n][1], dp[n][2]});
    }
    cout << ans << endl;
}