#include <fstream>
using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

int c = 1, n;
bool ciur[2000005];

int main() {
    fin >> n;
    for (int i = 4; i <= n; i += 2)
        ciur[i] = 1;
    for (int i = 3; i <= n; i += 2)
        if (!ciur[i]) {
            c++;
            for (int j = i * i; j <= n; j += i * 2)
                ciur[j] = 1;
        }
    fout << c;
}