#include <fstream>
using namespace std;

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

int n, i, j, k;
bool v[2000002];

int main() {
    fin >> n;
    fin.close();
    for (i = 3; i <= n; ++i) {
        if (!v[i]) {
            ++k;
            for (j = i + i; j <= n; j += i)
                v[j] = true;
        }
        ++i;
    }
    fout << k + 1;
    fout.close();
    return 0;
}