#include <fstream>
#include <vector>

using namespace std;

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

const int VALMAX = 2000000;

int N;

bool d[VALMAX + 5];
vector <int> primes;

void Ciur()
{
    if(N >= 2)
        primes.push_back(2);

    for(int i = 3; i * i <= N; i += 2)
        if(!d[i])
        {
            for(int j = i * i; j <= N; j += 2 * i)
                d[j] = 1;
        }

    for(int i = 3; i <= N; i += 2)
        if(!d[i])
            primes.push_back(i);
}

int main()
{
    fin >> N;

    Ciur();

    fout << primes.size() << '\n';

    return 0;
}