#include <stdio.h>
#include <algorithm>
int N;
int main(){
    //input
    scanf("%d",&N);
    int A[N];
    for (int i = 0;i < N;i++){
        scanf("%d",&A[i]);
    }

    //search
    int count = 0;
    for (int i = 0;i <= N-3;i++){
        if (A[i] != A[i+1] && A[i] != A[i+2] && A[i+1] != A[i+2]){
            //sort
            int tmp[3] = {A[i],A[i+1],A[i+2]};
            std::sort(tmp,tmp+3);

            //count
            if (tmp[1] == A[i] || tmp[1] == A[i+2]) count++;
        }
    }

    //ouput
    printf("%d\n",count);
    return 0;
}