#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

int main()
{
    vector<bool> ciur;
    int n, count = 1;

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

    fin>>n;
    ciur.resize(n+1);

    for(unsigned i = 3 ; i<=n ; i+=2) {
        if( ciur[i] == false ) {
            count++;
            for(unsigned k = i ; k<=n ; k+=i) {
                ciur[k] = true;
            }
        }
    }

    fout<<count;

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

    return 0;
}