import std.stdio, std.math, std.algorithm, std.array, std.string, std.conv, std.container, std.range;
T[] Reads(T)() { return readln.split.to!(T[]); }
alias reads = Reads!(int);

void scan(Args...)(ref Args args) {
    import std.conv : parse;
    string[] ss = readln.split;
    int i;
    foreach (ref arg ; args)
        arg = ss[i++].parse!int;
}

void main() {
    int n; scan(n);
    int[] d = reads.sort().array;
    int m = n/2;
    writeln(d[m] - d[m - 1]);
}
