#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

unsigned int v[2000005];
int main()
{
    int n,cont=0,i,j;
    fin>>n;
    for(i=2;i<=n;i++)
        v[i]=1;
    for(i=2;i<=n;i++)
 {
    if(v[i]==1){
        ++cont;
        for(j=2*i;j<=n;j+=i)
            v[j]=0;
   }
 }
 fout<<cont;

 return 0;
}