#include <fstream>

using namespace std;
    char prim[2000005];
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
int main(void)
{
    int i,j,n,nr;

    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    for (i=2; i<= n; ++i)
        prim[i] = 1;
    for (i=2; i<= n; ++i)
        if (prim[i])
        {
            ++nr;
            for (j = 2*i; j <= n; j=j+i)
                prim[j] = 0;
        }

    fout<<nr;

    return 0;
}