The determinant of a matrix 2 × 2 is defined as follows:

<image>

A matrix is called degenerate if its determinant is equal to zero. 

The norm ||A|| of a matrix A is defined as a maximum of absolute values of its elements.

You are given a matrix <image>. Consider any degenerate matrix B such that norm ||A - B|| is minimum possible. Determine ||A - B||.

Input

The first line contains two integers a and b (|a|, |b| ≤ 109), the elements of the first row of matrix A. 

The second line contains two integers c and d (|c|, |d| ≤ 109) the elements of the second row of matrix A.

Output

Output a single real number, the minimum possible value of ||A - B||. Your answer is considered to be correct if its absolute or relative error does not exceed 10 - 9.

Examples

Input

1 2
3 4


Output

0.2000000000


Input

1 0
0 1


Output

0.5000000000

Note

In the first sample matrix B is <image>

In the second sample matrix B is <image>
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Locale;
import java.io.IOException;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskH solver = new TaskH();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskH {
        private double[] sign = new double[]{1, -1};

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            double a = in.nextInt(), b = in.nextInt();
            double c = in.nextInt(), d = in.nextInt();

            double left = 0, right = 1e10;
            for (int i = 0; i < 200; ++i) {
                double mid = (left + right) / 2;
                double[] v1 = go(a, d, mid);
                double[] v2 = go(b, c, mid);

                if (v1[1] < v2[0] || v2[1] < v1[0]) left = mid;
                else right = mid;
            }

            Locale.setDefault(Locale.US);
            out.println(String.format("%.10f", left));
        }

        private double[] go(double a, double b, double x) {
            double min = 1e99, max = -1e99;
            for (double i : sign)
                for (double j : sign) {
                    min = Math.min(min, (a + i * x) * (b + j * x));
                    max = Math.max(max, (a + i * x) * (b + j * x));
                }
            return new double[]{min, max};
        }

    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (numChars == -1)
                throw new UnknownError();
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new UnknownError();
                }
                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public String next() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuffer res = new StringBuffer();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));

            return res.toString();
        }

        private boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

    }
}

