#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("prim.in");
ofstream fout("prim.out");
bool fv[2000005];

int main() {
    int n, nr_prime = 0;
    fin >> n;
    for (int i = 2; i * i <= n; i += 2) {
        for (int j = i * i; j <= n; j += i) {
            fv[j] = 1;
        }
        if (i == 2)
            --i;
    }
    for (int i = 2; i <= n; ++i)
        if (fv[i] == 0)
            ++nr_prime;
    fout << nr_prime;
    return 0;
}