import system'math;
import system'collections;
import system'routines;
import extensions;

extension op
{
    logTwo()
        = self.ln() / 2.ln();
}

public program()
{
    var input := console.readLine();
    var infoC := 0.0r;
    var table := new Dictionary();

    input.forEach:(ch)
    {
        var n := table[ch];
        if (nil == n)
        {
            table[ch] := 1
        }
        else
        {
            table[ch] := n + 1
        }
    };

    var freq := 0;
    table.forEach:(letter)
    {
        freq := letter.toInt().realDiv(input.Length);

        infoC += (freq * freq.logTwo())
    };

    infoC *= -1;

    console.printLine("The Entropy of ", input, " is ", infoC)
}