#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n, v[2000001], cnt;
int main()
{
    in >> n;
    v[1] = 1;
    v[0] = 1;
    for(int i = 2; i*i<=n; i++)
    {
        if(!v[i])
        {
            for(int j = 2; i*j<=n; j++)
                v[i*j] = 1;
        }
    }
    for(int i = 1; i<=n; i++)
        if(!v[i])
            ++cnt;
    out << cnt;
}