#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, fr[20000001], counter;
int main()
{
    fr[0] = 1;
    fr[1] = 1;
    fin >> n;
    for (int i = 2; i * i <= n; i++) {
        if (fr[i] == 0) {
            for (int j = i; j <= n / i; j++)
                fr[i * j] = 1;
        }
    }
    for (int i = 2; i <= n; i++) {
        if (!fr[i])
            counter ++;
    }
    fout << counter;
    return 0;
}