#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int main()
{int n,i,v[2000000],j,nr=0;
in>>n;
for (i=1;i<=n;i++)
    v[i]=i;
for (i=2;i*i<=n;i++)
    if (v[i]!=0)
       for (j=2*i;j<=n;j=j+i)
          v[j]=0;
for (i=2;i<=n;i++)
    if (v[i]!=0) nr++;
out<<nr;
    return 0;
}