#include <fstream>

using namespace std;

ifstream fi ("ciur.in");
ofstream fo ("ciur.out");
int N, c;
bool fr[2000000];

int main()
{
    fi >> N;
    for (int i = 2; i <= N; ++i)
    {
        if (!fr[i])
        {
            ++c;
            for (int j = 2; i*j <= N; ++j)
                fr[j*i]++;
        }
    }
    fo << c;
    return 0;
}