#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 = 1; 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;
}