const main = arg => {
    const input = arg.trim()
 
    const a = BigInt(input[0].split(" ")[0]);
    const b = BigInt(parseFloat(input[0].split(" ")[1])*100);
    let ret = a*b/100n
    console.log(String(ret).replace('n', ''))
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));  