#include <iostream>
#include <vector>
#include <fstream>
#include <algorithm>
#include <math.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout ("ciur.out");
char prim[2000005];
int main()
{ int n,nr=0,i,j;
    fin>>n;
 for(i=2;i<=n;++i)
   prim[i]=1;
 for(i=2;i<=n;++i)
    if(prim[i])
 {
     nr++;
     for(j=i+i;j<=n;j+=i)
        prim[j]=0;
 }
    fout<<nr;
}