#include <iostream>

using namespace std;

int main() {
	long long k, d, t, m, c, sol;

	cin >> k >> d >> t;

	long long nr = k / d;
	if(nr * d < k)
		m = (nr + 1) * d;
	else
		m = nr * d;

	c = (2LL * t) / (m + k);
	sol = c * m;

	t -= c * ((m + k) / 2);

	bool r = false;
	if((m + k) % 2 == 1) {
		t -= c / 2;
		if(c % 2 == 1) {
			t -= 1;
			r = true;
		}
	}

	if(t < k) {
		sol += t;
		cout << sol;
		if(r)
			cout << ".5";
	}
	else if(t == k) {
		sol += t;
		if(r)
			sol += 1;
		cout << sol << ".0";
	}
	else {
		sol += k;
		t -= k;
		sol += 2 * t;
		if(r)
			sol += 1;
		cout << sol << ".0";
	}

	return 0;
}