import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.SplittableRandom;
import java.util.InputMismatchException;
import java.io.IOException;
import java.io.InputStream;

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

    static class TaskC {
        public void solve(int testNumber, FastReader in, PrintWriter out) {
            Debug debug = new Debug(out);
            int n = 3;
            int[] a = in.nextIntArray(3);
            if (a[0] == a[1] && a[1] == a[2]) {
                out.println(0);
                return;
            }
            int max = Math.max(a[0], Math.max(a[1], a[2]));
            int minOP = -1;
            for (int i = max; i <= max + 2; ++i) {
                int[] b = a.clone();
                a = ArrayUtils.sort(a);

                int value = i;
                int op = (value - a[0]) / 2 + (value - a[1]) / 2 + (value - a[2]) / 2;
                a[0] += (value - a[0]) / 2 * 2;
                a[1] += (value - a[1]) / 2 * 2;
                a[2] += (value - a[2]) / 2 * 2;
                a = ArrayUtils.sort(a);
                if (a[0] == a[1] && a[1] == a[2] && a[2] == value) {
                    if (minOP == -1 || minOP > op)
                        minOP = op;
                } else if (a[2] == value && a[0] == a[1] && a[0] < a[2]) {
                    ++op;
                    if (minOP == -1 || minOP > op)
                        minOP = op;
                }
                a = b;
            }
            out.println(minOP);
        }

    }

    static class ArrayUtils {
        public static int[] sort(int[] a) {
            a = shuffle(a, new SplittableRandom());
            Arrays.sort(a);
            return a;
        }

        public static int[] shuffle(int[] a, SplittableRandom gen) {
            for (int i = 0, n = a.length; i < n; i++) {
                int ind = gen.nextInt(n - i) + i;
                int d = a[i];
                a[i] = a[ind];
                a[ind] = d;
            }
            return a;
        }

    }

    static class Debug {
        PrintWriter out;
        boolean oj;
        boolean system;
        long timeBegin;
        Runtime runtime;

        public Debug(PrintWriter out) {
            oj = System.getProperty("ONLINE_JUDGE") != null;
            this.out = out;
            this.timeBegin = System.currentTimeMillis();
            this.runtime = Runtime.getRuntime();
        }

        public Debug() {
            system = true;
            oj = System.getProperty("ONLINE_JUDGE") != null;
            OutputStream outputStream = System.out;
            this.out = new PrintWriter(outputStream);
            this.timeBegin = System.currentTimeMillis();
            this.runtime = Runtime.getRuntime();
        }

    }

    static class FastReader {
        private InputStream stream;
        private byte[] buf = new byte[8192];
        private int curChar;
        private int pnumChars;

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

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

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

        public int[] nextIntArray(int n) {
            int[] array = new int[n];
            for (int i = 0; i < n; i++) {
                array[i] = nextInt();
            }
            return array;
        }

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

    }
}



Measured memory_bytes: 23380