Wednesday, June 5, 2013

Codeforces Round #185 (Div. 2) B Archer

import java.io.*;
import java.math.*;
import java.util.*;

//Codeforces
public class MainCodeforces1 {
    private static MyScanner in;
    private static PrintStream out;
    private static boolean LOCAL_TEST = false;

    private static void solve() throws IOException
    {
        double a = in.nextInt();
        double b = in.nextInt();
        double c = in.nextInt();
        double d = in.nextInt();
        double probWin;
        double probZanoesLose = (d - c) / d;
        double totProbWin = 0;
        double probContinue = 1;
        while (true) {
            probWin = a / b * probContinue;
            double probLose = (1.0 - a / b) * probContinue;
            totProbWin += probWin;
            probContinue = (probLose * probZanoesLose);
            if (probWin < 1e-10)
                break;
        }
        out.println((double) totProbWin);
    }

    public static void main(String[] args) throws IOException {
        // helpers for input/output
        out = System.out;
        try {
            String cname = System.getenv("COMPUTERNAME");
            LOCAL_TEST = (cname.equals("ALPHA530"));
        } catch (Exception e) {
        }
        if (LOCAL_TEST) {
            in = new MyScanner("E:\\zin.txt");
        }
        else {
            boolean usingFileForIO = false;
            if (usingFileForIO) {
                // using input.txt and output.txt as I/O
                in = new MyScanner("input.txt");
                out = new PrintStream("output.txt");
            }
            else {
                in = new MyScanner();
                out = System.out;
            }
        }

        solve();
    }

    // =====================================
    static class MyScanner {
        Scanner inp = null;

        public MyScanner() throws IOException
        {
            inp = new Scanner(System.in);
        }

        public MyScanner(String inputFile) throws IOException {
            inp = new Scanner(new FileInputStream(inputFile));
        }

        public int nextInt() throws IOException {
            return inp.nextInt();
        }

        public long nextLong() throws IOException {
            return inp.nextLong();
        }

        public double nextDouble() throws IOException {
            return inp.nextDouble();
        }

        public String nextString() throws IOException {
            return inp.next();
        }

        public String nextLine() throws IOException {
            return inp.nextLine();
        }

    }

}

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