import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv,
    std.functional, std.math, std.numeric, std.range, std.stdio, std.string,
    std.random, std.typecons, std.container;

ulong MAX = 100_100, MOD = 1_000_000_007, INF = 1_000_000_000_000;
alias sread = () => readln.chomp();
alias lread(T = long) = () => readln.chomp.to!(T);
alias aryread(T = long) = () => readln.split.to!(T[]);
alias Pair = Tuple!(long, "x", long, "y");
alias PQueue(T, alias less = "a>b") = BinaryHeap!(Array!T, less);

void main()
{
    auto n = lread();
    auto route = new Pair[](n);
    foreach (ref e; route)
    {
        long x, y;
        scan(x, y);
        e = Pair(x, y);
    }

    real s = 0;
    auto iter = iota(n).array();
    do
    {
        foreach (i; iota(n - 1))
        {
            s += sqrt((abs(route[iter[i]].x - route[iter[i + 1]].x) ^^ 2 + abs(
                    route[iter[i]].y - route[iter[i + 1]].y) ^^ 2).to!real);
        }
    }
    while (iter.nextPermutation());
    n.product.writeln();
    writefln("%.15s", cast(real) s / n.product());
}

long product(long t)
{
    if (t == 1)
        return 1;
    else
        return t * product(t - 1);
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}
