#include <iostream>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

bool isColorat[2000001];

int main()
{
    int nrprim=0,n,i,j;
    f>>n;
    for (i=2;i<=n;i++){
        if (isColorat[i]==0){
            nrprim++;
            for (j=2*i;j<=n;j+=i)
                isColorat[j]++;
        }
    }
    g<<nrprim;
    return 0;
}