#include <iostream>
#include <string>
#include <iomanip>
using namespace std;

int main()
{
	std::string a;
	getline(std::cin, a);

	int n = a.size();
	long long c = 0, w = 0;
	double f = 0, fs = 0;

	for (int i = n - 1; i >= 0; --i) {
		if (a[i] == 'C') {
			w += n - i;
			f = c + fs;
		}
		else {
			c += n - i;
			f = w + fs;
		}
		f /= n - i;
		fs += f;
	}

	cout << setprecision(14) << f << endl;
}