import std.stdio;
import std.conv;
import std.string;
import std.math;

void main() {
    ulong[] input = readln.split.to!(ulong[]);
    ulong n = input[0];
    ulong m = input[1];
    ulong d = input[2];

    ulong sum = (n - d) * 2 * (pow(2, (m - 2))) * (m - 1);
    ulong c = (n - d) * (d == 0 ? 1 : 2);

    double ans = (c * (m - 1)).to!double / n / n * pow((2.0 / n.to!double), (m - 2));
    writeln(format("%.10f", ans));
}