#include <iostream>
#include <cstdio>
#include <vector>
using namespace std;

int main()
{
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	int n;
	cin >> n;
	vector<int> spf(n+1);
	vector<int> primes;
	for (int i = 2; i <= n; i++) {
		if (spf[i] == 0) {
			spf[i] = i;
			primes.push_back(i);
		}
		for (int j = 0; primes[j] <= spf[i] && i*primes[j] <= n; j++) {
			spf[i*primes[j]] = primes[j];
		}
	}
	printf("%d\n", primes.size());
}