#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
const int Nmax=2000000+5;
int n;
bool c[Nmax];
int main()
{
    f>>n;
    int nr=0;
    for(int i=2;i<=sqrt(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;
    g<<nr;
    return 0;
}