#include <fstream>
using namespace std;

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

const int NMax = 2000005;

int N, Sol;
bool Prim[NMax];

void Sieve()
{
    for(int i = 2; i<=N; i++)
        Prim[i] = 1;

    for(int i = 2; i<=N; i++)
        {
            if(Prim[i] == 1)
                {
                    Sol++;
                    for(int j = i+i; j<=N; j+=i)
                        Prim[j] = 0;
                }
        }

}

int main()
{
    fin>>N;

    Sieve();

    fout<<Sol<<"\n";

    return 0;
}