#include <iostream>
#include <fstream>

using namespace std;

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

int k;
long long n;
bool neprim[2000002] ;

void read()
{
    in>>n;
}

void solve()
{
    for(long long i = 2 ; i<=n;i++)
    {
        if(neprim[i] == false)
        {
            k++;
            for(long long i1 = i + i; i1<=n ;i1 = i1 + i)
            {
                neprim[i1] = true;
            }
        }
    }
}

void write()
{
    out<<k;
}
int main()
{
    read();
    solve();
    write();
}