#include <bits/stdc++.h>
using namespace std;

vector<size_t> sieve(size_t n) {
	vector<bool> isPrime(n + 1, true);
	isPrime[0] = isPrime[1] = false;

	vector<size_t> primes;
	for (size_t i = 2; i <= n; ++i)
		if (isPrime[i]) {
			primes.push_back(i);
			for (size_t j = 2 * i; j <= n; j += i)
				isPrime[j] = false;
		}

	return primes;
}

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
	
	size_t n;
	fin >> n;
	
	fout << sieve(n).size() << '\n';
}