#include <iostream>
#include <fstream>
using namespace std;
int c[2000005];

int ciur(int x)
{
    int cnt = 0;
    for (int i = 2; i <= x; i ++)
    {
        c[i] = 1;
    }
    for (int i = 2; i <= x; i ++)
    {
        if (c[i] == 1)
        {
            for (int j = i * 2; j <= x; j += i)
            {
                c[j] = 0;
            }
        }
    }
    for (int i = 2; i <= x; i ++)
    {
        if (c[i] == 1)
            cnt ++;
    }
    return cnt;
}

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n;
    in >> n;
    out << ciur(n) << "\n";
    return 0;
}