#include <fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int v[2000000];

int ciur(int n)
{
    int nr=0,i,j;
    for (i=2;i<n;i++)
  v[i]=1;
for (i=4;i<n;i+=2)
 v[i]=0;
 for(i=3;i<n;i+=2)
 {
     for(j=2*i;j<n;j+=i)
        v[j]=0;
 }
for (i=2;i<n;i++)
  if (v[i]==1)
    nr++;
return nr;
}
int main()
{
    int a;
    cin>>a;
    cout<<ciur(a);
    return 0;
}