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
#include <bits/stdc++.h>

using namespace std;

#define endl '\n'
#define st first
#define nd second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define ll long long
#define ld long double
ll mod=1000000007;
int inf=1000000007;
ll infl=1000000000000000007;

const int N=50007;

int DP[N][2];
int a[N];

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n,ans=inf;
    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i];
    for(int p=0;p<2;p++)
    {
        DP[1][1]=1,DP[1][0]=0;
        for(int i=2; i<=n; i++)
        {
            DP[i][1]=min(DP[i-1][0],DP[i-1][1])+1;
            DP[i][0]=DP[i-1][1];
            if(i%2==p&&a[i]>a[i-1]) DP[i][0]=min(DP[i][0],DP[i-1][0]);
            if(i%2!=p&&a[i]<a[i-1]) DP[i][0]=min(DP[i][0],DP[i-1][0]);
        }
        ans=min({ans,DP[n][0],DP[n][1]});
    }
    cout<<ans;
    return 0;
}