#include <iostream>
#include <fstream>

using namespace std;

int main()
{

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

    unsigned int a,i,s=1;

    fin>>a;

    unsigned int k[a+1];

    for (i=2;i<=a;i++) {

        k[i]=1;

    }

    for (i=3;i<=a;i+=2) {

        if (k[i]==1) {

            s++;

            for (int j=2*i;j<=a;j+=i) {

                k[j]=0;

            }

        }

    }

    fout<<s;

    fin.close();
    fout.close();

    return 0;
}