#include<bits/stdc++.h>
#define in f
#define out g
using namespace std;

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

int const maxsize = 2000010;

int n, k;
bool used[maxsize];

int main() {
    in >> n;
    for (int i = 2; i <= n; i++) {
        if (used[i] == false) {
            k++;
            for (int j = i; j <= n; j += i) {
                used[j] = true;
            }
        }
    }
    out << k;
}