#include<fstream>
#include <iostream>
using namespace std;
char prim[2000001];
long n,i,j,nr=0;
int main()
 {
ifstream f("ciur.in");
f>>n;
f.close();

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=j+i)
     prim[j]=0;
                             }
     ofstream g("ciur.out");
     g<<nr;
     g.close();
    return 0;
}