#include<stdio.h>

int main(void){

int i, N, A[100];
int counter=0;

scanf("%d",&N);

for(i=0;i<N;i++)
scanf("%d",&A[i]);

for(i=0;i<N-2;i++){
    
if( (A[i]!=A[i+1] && A[i+1]!=A[i+2] && A[i+2]!=A[i]) ) {
counter++;
if(((A[i]<A[i+1]) && (A[i+1]<A[i+2])) ||((A[i]>A[i+1]) && (A[i+1]>A[i+2])))
counter--;
}
}

printf("%d",counter);

return 0;

}