#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
const int Nmax=2000000+5;
int n;
bool c[Nmax];
int main()
{
    fin>>n;
    int nr=0;
    for(int i=2;i*i<=n;++i)
    {
        if(!c[i])
            for(int j=i*i;j<=n;j+=i)
                c[j]=1;
    }
    for(int i=2;i<=n;++i)
        if(!c[i])++nr;
    fout<<nr;
    return 0;
}