#include <fstream>

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000001];
int main()
{
    int n,i,j,nr=0;
    in>>n;
    for (i=2;i<=n;i++)
        if (v[i]==0)
            for (j=2;j*i<=n;j++)
                v[i*j]=1;
    for (i=2;i<=n;i++)
        if (v[i]==0)
            nr++;
    out<<nr;
    return 0;
}