const main = input =>{
    const nums = input.split('').map(n=>Number(n));
    const o_l = nums.filter(n=>n===1).length;
    const z_l = nums.filter(n=>n===0).length;
    console.log(Math.min(z_l,o_l)===0 ? 0 : Math.min(z_l,o_l)*2);
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));
