#include <iostream>
#include <cmath>
#include <string>

long double findN(long double eps) {
    int n = 1;
    while (( pow(2.0, n + 1) / pow(n + 2, n + 1)) - eps < std::numeric_limits<double>::epsilon()) {
        n++;
    }
    return n + 1;
}

int main() {
    long double eps;
    std::string str;
    std::cin >> str;

    eps = stold(str);

    auto N = findN(eps);

    double res = 0;
    double sum = 0;
    for (auto i = 1; i <= N; i++) {
        res = (pow((-1.0), i) * pow(2.0, i)) / pow(i + 1, i);
        sum += res;
    }

    std::cout.setf(std::ios_base::fixed, std::ios_base::floatfield);
    std::cout.precision(str.length() - 2);

    std::cout << sum << std::endl;
    return 0;
}