#include <iostream>
#include <fstream>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool ciur[50000001];
int main() {
    int n, counter = 0;
    fin >> n;
    for (int d = 2; d <= n; ++d) {
        if (ciur[d] == false) {
            for (int i = 2; i <= n / d; ++i) {
                ciur[i * d] = true;
            }
            ++counter;
        }
    }
    fout << counter;
    return 0;
}