#include<fstream>
using namespace std;
int n,i,j,nr;
int prim(int x)
{
    int j;
    for(j=2;j*j<=x;j++)
        if(x%j==0)
            return 0;
        return 1;

}

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;

    for(i=2;i<=n;i++)
        {
            if(prim(i))
        nr++;
        }
    g<<nr<<" ";

}