#include <bits/stdc++.h>

using namespace std;

int n, m;
double p;

double f(int r, int c) {
	if(r == n && c == m) return 0;
	if(r > n || c > m) return 1e20;

	double exp_down = f(r + 1, c);
	double exp_right = f(r, c + 1);

	double point_down;
	if(exp_right + p < exp_down) point_down = exp_right + p * 0.5;
	else if(exp_down < exp_right) point_down = exp_down;
	else {
		double dif = exp_down - exp_right;

		assert(exp_right <= exp_down);
		assert(dif <= p);

		point_down = (dif * exp_right + (p - dif) * exp_down + dif * dif * 0.5) / p;
	}

	double point_right;
	if(exp_down + p < exp_right) point_right = exp_down + p * 0.5;
	else if(exp_right < exp_down) point_right = exp_right;
	else {
		double dif = exp_right - exp_down;

		assert(exp_down <= exp_right);
		assert(dif <= p);

		point_right = (dif * exp_down + (p - dif) * exp_right + dif * dif * 0.5) / p;
	}

	double exp = 0.5 * (point_down + point_right);

	return exp;
}

int main() {
	cin >> n >> m >> p;

	cout << fixed << setprecision(12) << f(1, 1) << endl;
}