function main(input) {
  const K = parseInt(input, 10);
  let ans = 0;
  
  if (K % 2 === 0) {
    n = K / 2;
    ans = n * n;
  } else {
    n = Math.floor(K / 2);
    ans = n * (n + 1);
  }
  
  console.log(ans);
}

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