#include <fstream>

using namespace std;

int a[200000], n;

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