#include <cmath>
#include <fstream>
using namespace std;

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

const int NMax = 2000000;
bool prim[NMax];

int N, Nr;

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

    for(int i = 2; i <= N; i++)
        if(prim[i])
            {
                Nr++;
                for(int j = i + i; j <= N; j += i)
                    prim[j] = 0;
            }
}

int main()
{
    fin>>N;

    Ciur();

    fout<<Nr<<"\n";

    return 0;
}