#include <cstdint>
#include <iostream>
using namespace std;
int main() {
	uint64_t A, B, T;
	cin >> A >> B >> T;
	uint64_t result = 1LL << 60;
	for (uint64_t y = 0; y <= A && y <= (T + B - 1) / B; y++) {
		uint64_t x = int((T - B * y + A - 1) / A);
		uint64_t cost = A * x + B * y;
		if (cost < result) result = cost;
	}
	cout << result << endl;
}