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.OutputStream;
import java.io.PrintWriter;
import java.io.BufferedWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.io.Writer;
import java.io.OutputStreamWriter;
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);
        OutputWriter out = new OutputWriter(outputStream);
        TaskH solver = new TaskH();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskH {
        public void solve(int testNumber, InputReader in, OutputWriter out) {
            long a = in.readInt(), b = in.readInt(), c = in.readInt(), d = in.readInt();
            double low = 0, high = 1e25;
            for (int iter = 0; iter < 200; iter++) {
                double mid = (low + high) / 2;
                if (canIntersect(mid, a, b, c, d)) {
                    high = mid;
                } else {
                    low = mid;
                }
            }
            out.printLine(low);
        }

        private boolean canIntersect(double change, long a, long b, long c, long d) {
            DoubleDoublePair adRange = getRange(change, a, d);
            DoubleDoublePair bcRange = getRange(change, b, c);
            return adRange.second >= bcRange.first && adRange.first <= bcRange.second;
        }

        private DoubleDoublePair getRange(double change, long a, long b) {
            double low = a * b;
            double high = a * b;
            for (int aSign = -1; aSign <= 1; aSign += 2) {
                for (int bSign = -1; bSign <= 1; bSign += 2) {
                    double val = (a + aSign * change) * (b + bSign * change);
                    low = Math.min(low, val);
                    high = Math.max(high, val);
                }
            }
            return new DoubleDoublePair(low, high);
        }
    }
    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private InputReader.SpaceCharFilter filter;

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

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

        public int readInt() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return isWhitespace(c);
        }

        public static boolean isWhitespace(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }
    static class DoubleDoublePair implements Comparable<DoubleDoublePair> {
        public final double first;
        public final double second;

        public DoubleDoublePair(double first, double second) {
            this.first = first;
            this.second = second;
        }

        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }
            DoubleDoublePair pair = (DoubleDoublePair) o;
            return first == pair.first && second == pair.second;
        }

        public int hashCode() {
            int result = Double.hashCode(first);
            result = 31 * result + Double.hashCode(second);
            return result;
        }

        public String toString() {
            return "(" + first + "," + second + ")";
        }

        @SuppressWarnings ({"unchecked"})
        public int compareTo(DoubleDoublePair o) {
            int value = Double.compare(first, o.first);
            if (value != 0) {
                return value;
            }
            return Double.compare(second, o.second);
        }
    }
    static class OutputWriter {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream) {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer) {
            this.writer = new PrintWriter(writer);
        }

        public void print(Object... objects) {
            for (int i = 0; i < objects.length; i++) {
                if (i != 0) {
                    writer.print(' ');
                }
                writer.print(objects[i]);
            }
        }

        public void printLine(Object... objects) {
            print(objects);
            writer.println();
        }

        public void close() {
            writer.close();
        }
    }
}

