using System;
using System.Linq;
using System.Collections.Generic;

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            ABC120.C();
        }

        class ABC120
        {
            public static void A()
            {
                var ABC = Read.IntN();
                Console.WriteLine(Math.Min(ABC[2], ABC[1] / ABC[0]));
            }
            public static void B()
            {
                var A = Read.Int();
                var B = Read.Int();
                var K = Read.Int();
                int count = 0;
                for (int i = 100; i > 0; --i)
                {
                    if (A % i == 0 && B % i == 0)
                    {
                        count++;
                        if (K == count)
                        {
                            Console.WriteLine(i);
                            return;
                        }
                    }
                }
            }
            public static void C()
            {
                var S = Read.Str();
                var count0 = S.Count(c => c == '0');
                Console.WriteLine(Math.Min(count0, S.Length - count0) * 2);
            }
            public static void D()
            {
                var N = Read.Int();
                var M = Read.Int();
                var AB = Read.TupleInt(M);

                var UFT = new Util.UnionFindTree(N);
                List<long> inconvenient = new List<long>();
                long inc = (long)N * (N - 1) / 2;
                inconvenient.Add(inc);
                for(int i = M - 1; i >= 0; --i)
                {
                    var A = AB[i].Item1 - 1;
                    var B = AB[i].Item2 - 1;
                    if (!UFT.Same(A, B))
                    {
                        var sizeA = UFT.Count(A);
                        var sizeB = UFT.Count(B);
                        inc -= sizeA * sizeB;
                        UFT.Unite(A, B);
                    }
                    inconvenient.Add(inc);
                }
                inconvenient.Reverse();
                foreach (var v in inconvenient.Skip(1)) { Console.WriteLine(v); }
            }
        }
        class Util
        {
            public class UnionFindTree
            { //各Treeのサイズを保持する拡張仕様
                int[] parent;
                int[] count;
                public UnionFindTree(int n)
                {
                    parent = new int[n];
                    count = new int[n];
                    for(int i = 0; i < n; ++i) { parent[i] = i;count[i] = 1; }
                }
                public int Root(int i)
                {
                    if (parent[i] == i) { return i; } else { return parent[i] = Root(parent[i]); }
                }
                public int Count(int i) { return count[Root(i)]; }
                public bool Same(int i,int j) { return Root(i) == Root(j); }
                public void Unite(int i,int j)
                {
                    var ri = Root(i);
                    var rj = Root(j);
                    if (ri != rj) { parent[ri] = rj; count[rj] += count[ri]; }
                }
            }
        }

        static class Read
        {
            static Queue<string> queue = new Queue<string>();
            static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
            public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
            public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
            public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
            public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
            public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
            public static string[] StrN() { return Console.ReadLine().Split(' '); }
            public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
            public static long[,] LongMatrix(int r, int c)
            {
                var mat = new long[r, c];
                for (int i = 0; i < r; ++i)
                {
                    var x = Read.LongN();
                    for (int j = 0; j < c; ++j)
                    {
                        mat[i, j] = x[j];
                    }
                }
                return mat;
            }
            public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M)
            {
                Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new HashSet<int>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1]);
                    dict[ab[1]].Add(ab[0]);
                }
                return dict;
            }
        }
    }
}


Measured memory_bytes: 13364