#include <fstream>
#include <bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bitset<2000010> v;
int main()
{
    int n;
    in >> n;
    for(int i = 3 ; i*i<=n ; i++)
        if (v[i] == 0)
            for(int j = i*i ; j <=n ; j+= 2*i)
                v[j] = 1;
    int nr = 1;
    for(int i = 3 ; i <= n ; i+=2)
        if(v[i] == 0)
            nr++;
    out<<nr;

    return 0;
}