#include <fstream>

using namespace std;

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

int n,i,j,nrprim;
bool w[2000001];

int main()
{
    fin >> n;
    for (i=2; i<=n; i++)
        if (w[i] == 0)
        {
            nrprim++;
            for (j=i+i; j<=n; j+=i)
                w[j] = 1;
        }
    fout << nrprim;
    return 0;
}