#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,ciur[2000005]={0},d, j,nr=0;
int main()
{
    fin>>n;
    for (d = 2; d <= n; ++d)
        ciur[d] = 1;
    for (d = 2; d <= n; ++d)
        if (ciur[d])
        {
            ++nr;
            for (j = d+d; j <= n; j += d)
                ciur[j] = 0;
        }
    fout << nr;
    return 0;
}