#include <fstream>
#include <cmath>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");

    bool v[2000000];

int main()
{
    long long n;
    int x,i,j,nr=0;
    in>>x;
    for (i=2;i<=x;i++)
    {
        if (v[i]==0)
        {
            nr++;
        for (j=i+i;j<=x;j=j+i)
        v[j]=1;
        }
    }
    out<<nr;















    return 0;
}