#include <fstream>

using namespace std;
int n,i,prim[2000005],nrp,j;
int main()
{
    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])
        {
            ++nrp;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }
    fout<<nrp;
    return 0;
}