#include <iostream>
#include <fstream>
using namespace std;

bool E[2000005];
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int N,nrprim=0;
    in>>N;
    E[0]=1;
    E[1]=1;
    for(int i=2;i<=N;i++)
    {
        if(E[i]==0)
        {
            nrprim++;
            for(long long j=1LL*i*i;j<=N;j+=i)
                E[j]=1;
        }
    }
    out<<nrprim;
  return 0;


}