"""Sieve of Eratosthones.""" import math def sieve(n): """Sieve of Eratosthones.""" l = [True] * (n + 1) prime = [] start = 2 end = int(math.sqrt(n)) while start <= end: if l[start] is True: prime.append(start) for i in range(start * start, n + 1, start): if l[i] is True: l[i] = False start += 1 for j in range(end + 1, n + 1): if l[j] is True: prime.append(j) return prime if __name__ == "__main__": print(sieve(int(input("Enter n: ").strip())))