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#include <cstdio>
#include <algorithm>

int vol[60000];

int main() {
    int N;
    int resup=0;
    int resdown=0;

    scanf("%d\n", &N);
    for (int i=0; i<N; ++i) {
        int v;
        scanf("%d", &v);
        vol[i] = v;
    }

    int last = vol[0];
    for (int i=1; i<N; ++i) {
        if ((i%2)==1) { //up
            if (vol[i]<=last) {
                resup++;
                last = 1000001;
            } else {
                last = vol[i];
            }
        } else { //down
            if (vol[i]>=last) {
                resup++;
                last = -1000001;
            } else {
                last = vol[i];
            }
        }
    }

    last = vol[0];
    for (int i=1; i<N; ++i) {
        if ((i%2)==0) { //up
            if (vol[i]<=last) {
                resdown++;
                last = 1000001;
            } else {
                last = vol[i];
            }
        } else { //down
            if (vol[i]>=last) {
                resdown++;
                last = -1000001;
            } else {
                last = vol[i];
            }
        }
    }

    printf("%d\n", (int)std::min(resdown, resup));
    return 0;
}