#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <functional>
#include <numeric>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#define bogo_sort std::sort
#define bozo_sort std::stable_sort
#define alles(obj) obj.begin(), obj.end()
#define elif else if
#define unless(flg) if(!(flg))
#define elless(flg) else if(!(flg))
#define echo std::cout <<
#define read std::cin >>
#define endl std::endl
#define fin << '\n'
#define bash push_back
#define makePair std::make_pair
#define _ << ' ' <<
// type-define
#define Stack std::stack
#define Queue std::queue
#define Set std::set
#define PQueue std::priority_queue
#define Vector std::vector
#define Pair std::pair
#define Map std::map
#define HashMap std::unordered_map
#define Greater std::greater
using String = std::string;
using llong = long long;
using boolean = bool;
using Pii = Pair<int, int>;
using Vi = Vector<int>;
using Vii = Vector<Pii>;
// utils
constexpr int dx[] = {1, 0, -1, 0, 1, 1, -1, -1};
constexpr int dy[] = {0, 1, 0, -1, 1, -1, 1, -1};
constexpr int INF = 0x3f3f3f3f;
constexpr llong LINF = 0x3f3f3f3f3f3f3f3fLL;

namespace {
    template<class A, class B> A power ( llong x, llong n, llong mod ) {
        llong ans = 1;
        while ( n > 0 ) {
            if ( n & 1 ) ans = ( ans * x ) % mod;
            x = ( x * x ) % mod;
            n >>= 1;
        }
        return ans;
    }
    template<class A, class B> A power ( A x, B n ) { return power( x, n, 1000000007 ); }
    template<class A> A gcd ( A x, A y ) { return x % y ? gcd( y, x % y ) : y; }
    template<class A, class B> A lcm ( A x, B y ) { return ( x / gcd(x, y) * y ); }
//    template<class A> inline A abs ( A n ) { return ( n < 0 ) ? -n : n; }
    template<class A, class B> inline bool chmax ( A &a, const B &b ) { return b > a ? a = b, true : false; }
    template<class A, class B> inline bool chmin ( A &a, const B &b ) { return b < a ? a = b, true : false; }
    boolean isMovable ( int x, int y, int w, int h ) {
        return ( x >= 0 && y >= 0 && x < w && y < h );
    }
}

namespace Rlyeh {

    struct UnionFind {

        Vi data;

        UnionFind(int n) {
            data.resize(n+5, -1);
        }

        boolean unite(int x, int y) {
            int rootX = getRoot(x);
            int rootY = getRoot(y);
            if ( rootX == rootY ) return false;
            if ( data[rootX] < data[rootY] ) std::swap(rootX, rootY);
            data[rootX] += data[rootY];
            data[rootY] = rootX;
            return true;
        }

        int getRoot(int i) {
            return ( data[i] < 0 ) ? i : ( data[i] = getRoot(data[i]) );
        }

        int getSize(int n) {
            return -data[getRoot(n)];
        }

        boolean isUnited(int x, int y) {
            return (getRoot(x) == getRoot(y));
        }
    };

#define int llong

    signed call_of_Cthulhu( signed datum ) {

        String s;
        read s;
        int n = s.size();
        int a = 0, b = 0;
        for ( int i = 0; i < n; i++ ) {
            if ( s[i] == '0' ) a++;
            else b++;
        }
        echo std::min(a, b)*2 fin;

        return 0;
    }
}

signed main(){std::cin.tie(0); std::ios::sync_with_stdio(false); int main_result = Rlyeh::call_of_Cthulhu(114514); return 0;}


Measured memory_bytes: 512