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