#include <fstream>

using namespace std;

int a[2000006], n;
int prime[11000], k;

int main()
{
    int i, j;
    ifstream fin("ciur.in");
    fin >> n;
    fin.close();
    for(i = 3; i * i <= n; i += 2)
        if(a[i] == 0)
            for(j = i * i; j <= n; j = j + 2 * i)
                a[j] = 1;
    k = 0;
    prime[++k] = 2;
    for(i = 3; i <= n; i += 2)
        if(a[i] == 0)
            prime[++k] = i;
    ofstream fout("ciur.out");
    fout << k << "\n";
    fout.close();
    return 0;
}