#include <iostream>
#include <cmath>
using namespace std;

int main(){
	double exponent = M_E, a = sqrt(2)/exponent, sum = 0, E;
	cin >> E; 
	for (int i = 1; (a = sqrt(i+1)/(i * exponent)) >= E; i++){
		exponent *= M_E;
		sum += a;
	}
	cout << sum;
	return 0;
}