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#include <cstdio>
#include <algorithm>


int comp(int a, int b, int par, int expPar) {
    if (a <= b && par == expPar) return 1;
    if (b <= a && par != expPar) return 1;

    return 0;
}

int main() {
    int n;
    scanf("%d\n", &n);

    int changes[2] = {0, 0};
    bool skip[2] = {false, false};

    int prevVal, val;

    scanf("%d", &val);
    for (int i=1; i<n; i++) {
        prevVal = val;
        scanf("%d", &val);

        for (int k=0; k<2; k++) {
            if (skip[k]) skip[k] = false;
            else if (comp(prevVal, val, i % 2, k)) {
                changes[k]++;
                skip[k] = true;
            }
        }
    }

    printf("%d", std::min(changes[0], changes[1]));
}