#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

vector <int> primality;

int main()
{
    int N;
    fin >>N;

    primality.resize(N+1);

    for (int i = 2; i <= N; ++i)
		primality[i] = 1;

	int counter = 0;
	for (int i = 2; i <= N; ++i)
		if (primality[i])
		{
			++counter;
			for (int j = i+i; j <= N; j+=i)
				primality[j] = 0;
		}

	fout <<counter <<'\n';

    return 0;
}