#include <fstream>
#include <vector>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int limita, i, j;
int main()
{
    fin >> limita;
    vector <bool> ciur;
    ciur.assign(limita+1, 0);
    for (i = 2; i <= limita; i++)
    {
        if (ciur[i]== 0)
            for (j = i * 2; j <= limita; j += i)
                ciur[j] = 1;
    }
    int cate = 0;
    for (i = 2; i <= limita; i++)
        if (ciur[i] == 0)
            cate++;
    fout << cate;
    return 0;
}