#include <iostream>
#include <fstream>

int v[2000000];

int main() {
    std::ifstream fin("ciur.in");
    std::ofstream fout("ciur.out");
    int nr = 0, n;
    fin >> n;
    for(int i = 2; i <= n; ++i) {
        if(v[i] == 0) {
            nr++;
            for (int j = i * i; j <= n; j += i) {
                v[j] = 1;
            }
        }
    }

    fout << nr;

    fin.close();
    fout.close();
    return 0;
}