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

using namespace std;

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

int n, c[nmax], sol;

void eratostene(){
    fin >> n;
    for(int i = 2; i <= n; ++i)
        c[i] = 1;
    for(int i = 2; i <= n; ++i)
        if(c[i] == 1){
            sol++;
            for(int j = 2; j * i <= n; j++)
                c[i * j] = 0;
        }
    fout << sol;
}

int main(){

    eratostene();
    fin.close();
    fout.close();
    return 0;
}