#include <iostream>
#include <fstream>

#define lim 2000001

using namespace std;

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

char ciur[lim];
int n;

void umpleCiur(int x)
{
    int xx=x;
    while(xx<=n)
    {
        ciur[xx]=1;
        xx+=x;
    }
}

int main()
{
    int i=2;
    int contor=0;
    fin>>n;
    while(i<=n)
    {
        if(!ciur[i])
        {
            contor++;
            umpleCiur(i);
        }
        i++;
    }
    fout<<contor;
    return 0;
}