#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
int N,nr=0;
in>>N;
bool ciur[N+1];
fill(ciur,ciur+N,0);
for(unsigned i=2;i<=N;i++)
{
    if(ciur[i]==0)
    {
        nr++;
         for(unsigned j=i+i;j<=N;j+=i)
        {
            ciur[j]=1;
        }
    }
}

out<<nr;
out.close();
    return 0;
}