A.cpp

#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;

#define rep(i, a, b) for (auto i = (a); i < (b); ++i)
#define per(i, a, b) for (auto i = (b); i-- > (a); )
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) int((x).size())
#define lb(x...) lower_bound(x)
#define ub(x...) upper_bound(x)

template<class T> bool ckmin(T& a, const T& b) { return a > b ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	ll k, d, t; cin >> k >> d >> t;
	ll p = (k + d - 1) / d * d;
	ll c = k + p;
	ll rem = (2 * t) % c;
	ld fin = (2 * t) / c * p;
	if (rem > 2 * k) fin += rem - k;
	else fin += rem / 2.0;
	cout << fixed << setprecision(1) << fin << '\n';
}