#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int NMAX = 2000000;bool c[NMAX];int n,cnt = 1;
void ciur()
{
    c[0] = c[1] = true;
    for(int i = 3; i <= n; i+=2)
        if(c[i] == false)
        {
            ++cnt;
            for(int j = i+i; j <= n; j+=i) c[j] = true;
        }
}

int main()
{
   in>>n;ciur();out<<cnt;
}