double cos(double x) {
    return 1 + help_cos(x, 2, -1);
}
double factorial(int x);
double pow(int x, int y);
double help_cos(double x, long i, short side) {
    const double bot = 1/1000000;
    double sum = pow(x, i) / factorial(i);
    if (sum < 1/bot) return side*sum;
    return (side*sum + help_cos(x, i*2, -1*side));
}