#include <stdio.h>

int main(void){
    int i, min, max, N, ans = 0;
    scanf("%d", &N);
    int a[N];
    scanf("%d %d", &a[0], &a[1]);
    for(i=0;i<N-2;i++){
        scanf("%d", &a[i+2]);

        min = a[i], max = a[i+1];
        if(a[i+1]<min) min = a[i+1];
        if(a[i+2]<min) min = a[i+2];
        if(a[i]>max)   max = a[i];
        if(a[i+2]>max) max = a[i+2];

        if(a[i]!=a[i+1] && a[i+1]!=a[i+2] && a[i+2]!=a[i]){
            if((a[i]!=min && a[i]!=max)||(a[i+2]!=min && a[i+2]!=max)){
                ans++;
            }
        }
    }
    printf("%d\n", ans);
    return 0;
}