#include <fstream>

const int N = 2000001;
bool c[N];

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");

int main()
{
    int i, j, n,nr;
    in>>n;
    for (i=2; i*i<N; i++)
    {
        if (not c[i])
            for (j=i*i; j<N; j+=i)
            c[j]=true;
    }
    nr=0;
    for (i=2; i<=n; i++)
        if (not c[i])
        nr++;
    out << nr;
    return 0;
}