#include <fstream>
using namespace std;
int n, i, j, prime, pr[1000000];
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin >> n;
    for (i=2;i*i<=n;i++) {
        if (pr[i]==0) {
            prime++;
            for (j=2;i*j<=n;j++) {
                pr[i*j] = 1;
            }
        }
    }
    fout << prime;
    return 0;
}