// http://infoarena.ro/problema/ciur
#include <fstream>
#include <vector>
using namespace std;

#define maxSize 2000001

int primeNumbers;
vector<bool> isPrime(maxSize,true);

ifstream in("ciur.in");
ofstream out("ciur.out");

int main() {
	int limit;

	in >> limit;

	for(int i=2;i<=limit;i++)
		if(isPrime[i]) {
			for(int k=i;k<=limit;k=k+i)
				isPrime[k] = false;

			primeNumbers++;
		}

	out << primeNumbers;

	in.close();
	out.close();

	return (0);
}