#include<fstream>
using namespace std;

ifstream fin("erat.in");
ofstream fout("erat.out");
bool ok[30000000];
int i, n, j;
int k;

int main()
{
    fin >> n;
    for (i = 0; i < n; i++)
        ok[i] = true;
    for ( i= 2; i*i <= n; i++)
        if (ok[i])
        {
            j = 2;
            while (i*j <= n)
            {
                ok[i*j] = false;
                j++; 
            }
        }        
    for (i = 2; i <= n; i++)
        if (ok[i])
            k++;
               
    fout << k;
    fout << '\n'; 
    fin.close();
    fout.close();
    return 0;
}