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#include "bits/stdc++.h"
 
using namespace std;

template<typename _T> void _debug(const char *s, _T x){ cerr << s << " = " << x << "\n";}
template<typename _T, typename... R> void _debug(const char *s, _T x, R... r){ while(*s != ',') cerr << *s++; cerr << " = " << x << ", "; _debug(s + 1, r...);}
 
#define debug(...)  _debug(#__VA_ARGS__,  __VA_ARGS__);
 
#define sz(s)   int32_t(s.size())
 
using ll = long long;
using ld = long double;

#define int ll

const int INF = 1e6;

int32_t main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n;  cin >> n;
    vector < int > arr(n), brr(n), crr(n);
    for(int i = 0; i < n; i++){
        cin >> arr[i];
        crr[i] = brr[i] = arr[i];
    }
    int ans = INF;  // 0 -> ma roscnąć, 1 -> ma maleć
    for(int i = 1; i < n; i++){
        if(i % 2 == 0){
            if(brr[i - 1] >= brr[i])    brr[i] = +INF;
            if(crr[i - 1] <= crr[i])    crr[i] = -INF;
        }
        if(i % 2 == 1){
            if(brr[i - 1] <= brr[i])    brr[i] = -INF;
            if(crr[i - 1] >= crr[i])    crr[i] = +INF;
        }
    }
    int cnt_b = 0, cnt_c = 0;
    for(int i = 1; i < n; i++){
        if(i % 2 == 0){
            if(brr[i - 1] >= brr[i])    cnt_b = INF;
            if(crr[i - 1] <= crr[i])    cnt_c = INF;
        }
        if(i % 2 == 1){
            if(brr[i - 1] <= brr[i])    cnt_b = INF;
            if(crr[i - 1] >= crr[i])    cnt_c = INF;
        }
        if(arr[i] != brr[i])    cnt_b++;
        if(arr[i] != crr[i])    cnt_c++;
    }
    ans = min(cnt_b, cnt_c);
    cout << ans << "\n";
}