#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int N,p,q,prim[200005],cnt;
int l;

int main ()
{f>>N;
 for (int i = 2; i <= N; ++i)
        prim[i] = 1;
    for (int i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (int j = i+i; j <= N; j += i)
                prim[j] = 0;
        }
cout<<cnt<<" ";
}