#include <fstream>
#include <math.h>
#include <iostream>
using namespace std;
int M,N,x,i,A[2000030];

int main () {
    ifstream in;
    in.open("ciur.in");
    in >> N;
    for (i=2; i<=N;i++)
    A[i]=1;
        for (x=2;x<=N;x++)
            if (A[x]) {
                M++;
                for (i=x+x; i<=N; i=i+x)
                    {
                        A[i]=0;
                    }
            }
    ofstream out;
    out.open("ciur.out");
    out << M;
    out.close();
}