#include <iostream>
#include <bitset>
#include <fstream>
using namespace std;

#define MAXN 1000005

int count_primes_under(const int n){
    bitset<MAXN> e_prim;
    e_prim.set();
    int rez = 1, i = 3; /* 2 */
    for( ; i*i <= n; i += 2){
        if(e_prim[i/2]){
            ++rez;
            for(int j = i*i; j <= n; j += 2*i){
                e_prim[j/2] = 0;
            }
        }
    }
    for( ; i <= n; i += 2){
        if(e_prim[i/2]){
            ++rez;
        }
    }
    return rez;
}

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n;
    f >> n;

    g << count_primes_under(n);
    return 0;
}