#include <fstream>

using namespace std;

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

bool v[2000001];

int main()
{
    int n, i, j, nr = 2, nrp = 0;
    fin >> n;
    for(i = 1; nr <= n; i++)
    {
        if(v[nr] == 0)
        {
            nrp++;
            for(j = nr*2; j <= n; j += nr)
                v[j] = 1;
        }
        nr++;
    }
    fout << nrp;
    return 0;
}