#include <iostream>
#include <fstream>
#define nmax 2000000

using namespace std;

int n;
bool p[nmax];
#define p (p-2)

int main()
{
    ifstream in("ciur.in");
    in >> n;
    in.close();
    int s=0;
    for(int i=2;i<=n;++i) p[i] = 1;
    for(int i=4;i<=n;i+=2)  p[i] =0;
    for(int i=3;i*i<=n;i+=2)
        for(int j=i*i;j<=n;j+=2*i) p[i] =0;
    for(int i=2;i<=n;++i)
        s+=p[i];
    ofstream out("ciur.out");
    out << s;
    out.close();
    return 0;
}