#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool mat[2000001];
int main ()
{
    int n, sum = 0;
    fin >> n;
    for (int i = 2; i <= n; i++)
        if (mat[i] == false)
        {
            sum += 1;
            for (int j = i+i; j <= n; j+=i)
                mat[j] = true;
        }
    fout << sum;
    fin.close();
    fout.close();
    return 0;
}