function main(input) {
  input = input.split('\n');
  let line = input[0].split(' ');
  let a = BigInt(line[0]);
  let b = BigInt(line[1].replace('.', ''));
  let r = (a * b) / 100n;
  console.log(r + '');
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));
