#include <fstream>
using namespace std;
unsigned int N, count_prime;
bool sieve[2000000];

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

int main()
{
    cin>>N;
    cin.close();
    for(unsigned int i = 2; i <= N; i++)
    {
        if(sieve[i] == false)
        {
            for(unsigned int j = i; j <= N; j += i)
                sieve[j] = true;

            sieve[i] = false;
            count_prime++;
        }
    }
    cout<<count_prime;
    cout.close();
    return 0;
}