import std.stdio,
       std.conv,
       std.string,
       std.range,
       std.math,
       std.algorithm;

void main()
{
    auto N = readln.strip.to!int;
    auto A = readln.split.to!(int[]);

    iota(2, A.length)
        .count!(i=>A[i-2]<A[i-1]&&A[i-1]>A[i]&&A[i-2]!=A[i]
                 ||A[i-2]>A[i-1]&&A[i-1]<A[i]&&A[i-2]!=A[i])
        .writeln;
}