#include <cmath>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    int x,N,k=0,i,ok=0;
    out<<"N= ";in>>N;
    for(i=2;i<=N;i++)
    {
        ok = 1;
        for(x=2;x*x<=i;x++)
            if (i % x == 0)
                ok = 0;
        if (ok)
            k++;

    }
    out<<k;
return 0;
}