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

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

int n, i, j, k;
bitset<2000002> v;

int main() {
    fin >> n;
    fin.close();
    for (i = 3; i <= n; i += 2)
        if (!v[i]) {
            ++k;
            for (j = i + i; j <= n; j += i)
                v[j] = 1;
        }
    fout << k + 1;
    fout.close();
    return 0;
}