Зимовец - 3

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

double Calc(double x, double epsilon){
    double a = - x;
    int i = 1;
    double res = 0;
    while(abs(a) > epsilon){
        res+=a;
        i++;
        a*= - (x*x) / ( (3*i+1) * (3*i+2) * (3*i+3) );
    }
    return res;
}
int main() {
    double x,res,epsilon;
    cin >> x >> epsilon;
    res = Calc(x,epsilon);
    cout << res;
}