import java.io.*; import java.util.*; public class Main_yukicoder713 { private static Scanner sc; private static Printer pr; private static void solve() { int n = sc.nextInt(); Prime prime = new Prime(n); int ans = 0; for (int p : prime) { ans += p; } pr.println(ans); } static class Prime implements Iterable { private int n; private BitSet p; Prime(int n) { this.n = n; p = new BitSet(n / 2); int m = (int)Math.sqrt(n); // for (int i = 1; i <= m; i++) { for (int bi = p.nextClearBit(0); 2 * (bi + 1) + 1 <= m; bi = p.nextClearBit(bi + 1)) { long i = bi + 1; // if (p.get(i - 1)) { // continue; // } for (long j = 2 * i * (i + 1); 2 * j + 1 <= n; j += 2 * i + 1) { p.set((int)(j - 1)); } } } boolean isPrime(int n) { if (n == 2) { return true; } if (n == 1 || (n & 0x1) == 0) { return false; } return !p.get(n / 2 - 1); } List getPrimeList() { List ret = new ArrayList<>(); for (int p : this) { ret.add(p); } return ret; } Map primeFactorize(long x) { Map hm = new TreeMap<>(); long n = x; for (int p : this) { if ((long)p * p > n) { break; } int cnt = 0; while (n % p == 0) { cnt++; n /= p; } if (cnt > 0) { hm.put((long)p, cnt); } } if (n != 1) { hm.put(n, 1); } return hm; } @Override public Iterator iterator() { return new PrimeIterator(); } private class PrimeIterator implements Iterator { int index; PrimeIterator() { index = -1; } @Override public boolean hasNext() { if (index == -1) { return n >= 2; } else { return 2 * (index + 1) + 1 <= n; } } @Override public Integer next() { if (index == -1) { if (n >= 2) { index = p.nextClearBit(0); return 2; } else { throw new NoSuchElementException(); } } else { int ret = 2 * (index + 1) + 1; if (ret <= n) { index = p.nextClearBit(index + 1); return ret; } else { throw new NoSuchElementException(); } } } } static boolean isPrime(long n) { if (n == 2) { return true; } if (n == 1 || (n & 0x1) == 0) { return false; } for (long i = 3; i * i <= n; i += 2) { if (n % i == 0) { return false; } } return true; } } // --------------------------------------------------- public static void main(String[] args) { sc = new Scanner(INPUT == null ? System.in : new ByteArrayInputStream(INPUT.getBytes())); pr = new Printer(System.out); solve(); // pr.close(); pr.flush(); // sc.close(); } static String INPUT = null; private static class Printer extends PrintWriter { Printer(OutputStream out) { super(out); } } }