#include <iostream>
#include <fstream>
#define nmax 2000005

using namespace std;

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

int n,k=0;
bool v[nmax];

void ciur(){
    for (int i=2; i<=n; i++) {
        if (v[i]==0) {
            k++;
            for (int j=2*i; j<=n; j+=i) v[j]=1;
        }
    }

    out << k;

}

int main()
{
    in >> n;
    ciur();
    return 0;
}