CF_TR5_A

// CF_TR5_A
#define _CRT_SECURE_NO_WARNINGS
#define M_PI 3.1415926535897932384626433832795
#include <iostream>
#include <stdio.h>
#include <fstream>
#include <math.h>

using namespace std;

int main()
{
    long double x, y;
    ifstream file_in("angle1.in");
    file_in >> x >> y;
    file_in.close();

    long double ang = 0;
    if ((x > 0) && (y >= 0)) ang = atan2(y, x);
    if ((x > 0) && (y < 0)) ang = atan2(y, x) + 2 * M_PI;
    if (x < 0) ang = atan2(y, x) + M_PI;
    if ((x == 0) && (y > 0)) ang = M_PI / 2;
    if ((x == 0) && (y < 0)) ang = 3 * M_PI / 2;

    ofstream file_out("angle1.out");
    file_out << ang;
    file_out.close();

    //system("pause");
    return 0;
}