#include <iostream>
#include <iomanip>

int main() {
    int x;
    std::cin >> x;
    double average = (x + 0.8 * x + 0.9 * x) / 3;
    std::cout << std::fixed << std::setprecision(1) << average << std::endl;
    return 0;
}    
/**************************************************************
	Problem: 1613
	User: fuyijun
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/