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#include <algorithm>
#include <cstdio>
using namespace std;

const int FIRSTNEG = 0;
const int FIRSTPOS = 1;
const int NCHANGD = 0;
const int CHANGED = 1;
const int maxN = 5e4 + 10;

int dp[maxN][2][2];
int t[maxN];

void calc(int i, int first) {
    bool should_be_pos = (i % 2 == 0) ^ (first == FIRSTPOS);
    bool both_unchanged_possible = (should_be_pos && t[i] > t[i - 1]) ||
                                   (!should_be_pos && t[i] < t[i - 1]);

    dp[i][first][CHANGED] =
        1 + min(dp[i - 1][first][CHANGED], dp[i - 1][first][NCHANGD]);
    dp[i][first][NCHANGD] = dp[i - 1][first][CHANGED];
    if (both_unchanged_possible)
        dp[i][first][NCHANGD] = dp[i - 1][first][NCHANGD];
}

int main() {
    int N;
    scanf("%d", &N);
    for (int i = 0; i < N; ++i)
        scanf("%d", t + i);

    for (int i = 0; i < 2; ++i)
        dp[0][i][CHANGED] = 1;
    for (int i = 1; i < N; ++i) {
        calc(i, FIRSTNEG);
        calc(i, FIRSTPOS);
    }

    int result = dp[N - 1][FIRSTNEG][CHANGED];
    for (int i = 0; i < 2; ++i)
        for (int j = 0; j < 2; ++j)
            result = min(result, dp[N - 1][i][j]);
    printf("%d\n", result);
    return 0;
}