#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
const int NMAX=2000001;
int prim[NMAX],N,i,nr;
void marcare()
{
    for(int j=i;j<=N;)
    {
        j=j+i;
        prim[j]=1;
    }
}
int main()
{
    fin>>N;
    for(i=2;i<=N;++i)
        if(prim[i]==0)
            marcare(),++nr;
    fout<<nr;
    return 0;
}