#include <iostream>
#include <cmath>
using namespace std;
int main() {
	float sum = 0, e, next;
	next = -1 / 6;
	int i = 4;
	cin >> e;
	while (fabs(next) >= e) {
		sum += next;
		next *= -(i - 3) / i;
		++i;
	}
	cout << "S = " << sum << "\n";
	system("pause");
	return 0;
}