#include <fstream>
#define len 2000001

using namespace std;

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

unsigned N, count = 1;
bool ciur[len];

int main()
{
    in >> N;
    for(unsigned i = 3; i <= N; i += 2)
        if(!ciur[i])
        {
            ++count;
            unsigned k = 2;
            while(i * k <= N)
            {
                ciur[i * k] = true;
                ++k;
            }
        }
    out << count;
    return 0;
}