const main = input => {
  const K = parseInt(input.trim())
  if (K % 2 === 0) {
    console.log((K / 2) * (K / 2))
  } else {
    console.log(Math.ceil(K / 2)) * ((K - 1) / 2)
  }
}
// 標準入力
main(require("fs").readFileSync("/dev/stdin", "utf8"));
