#include <fstream>

using namespace std;

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



int main()
{
    int n;
    fin >> n;
    bool t[2000005];
    for(int i = 2; i <= n/2; i++ ){
        if( t[i] == 0 )
        {
            int j = i + i;
            while(j <= n)
            {
                    t[j] = 1;
                    j = j + i;
            }
        }
    }

    int total = 0;

    for(int i = 2; i <= n; i++)
        if( t[i] == 0 ) total++;

    fout << total;
}