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#include <bits/stdc++.h>
#define FOR(i,n) for(int i = 0; i<n; ++i)
#define FOREACH(v, a) for(auto & v : (a))
#define X first
#define Y second
#define PR std::pair
#define MPR std::make_pair
#define ReversePQ(type) priority_queue<type,vector<type>, std::greater<type>> 
#define PQ(type) priority_queue<type>
typedef long long ll;
typedef std::vector<int> VI;


using namespace std;

#pragma region Ready functions

int fastPower(int a, int b){
    int res=1, pop_a = a;
    while(b){
        if(b&1) res *= pop_a;
        pop_a *= pop_a;
        b>>=1;
    }
    return res;
}

#pragma endregion

int countChanges(vector<int> nums, bool growing){

    int changes = 0;

    for(int i = 1; i<nums.size(); i++){

        if(growing){
            if(nums[i - 1] >= nums[i]){
                nums[i] = INT_MAX;
                changes++;
            }
        }
        else{
            if(nums[i-1] <= nums[i]){
                nums[i] = INT_MIN;
                changes++;
            }
        }
        growing = !growing;
    }

/*
    for(int i : nums){
        cout<<i<<" ";
    }
    cout<<endl;
*/
    return changes;
}

void solve(){

    int n;
    cin>>n;
    vector<int> growth;
    for(int i = 0; i<n; i++){
        int x;
        cin>>x;
        growth.push_back(x);
    }
    
    cout<<(min(countChanges(growth, false), countChanges(growth, true)));

    

}

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    
    solve();
}