ser

#include <iostream>
#include <math.h>

using namespace std;

int main(void) {
    double S = 1, elem = 1, eps;
    cin >> eps;
    for (int i = 0; fabs(elem) > eps; ++ i) {
        elem *= -1 / ((2.0 * i + 2) * (2.0 * i + 3));
        S += elem;
    }
    cout << S << endl;
    return 0;
}