#include <bits/stdc++.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
    int n, rez = 1;
    f >> n;
    vector<bool> v(n + 1, 0);
    for (int i = 3; i <= n; i += 2)
        if (!v[i])
        {
            rez++;
            for (int j = 2; i * j <= n; j++)
                v[i * j] = 1;
        }
    g << rez;
    return 0;
}