#include <fstream>
 
char prim[2000005];
 
using namespace std;
 
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
 
    int N,k=1,i,j;
 
    fin>>N;
 
    for(i=3;i<=N;i+=2)  {
     if(!prim[i]){k++;
			   for(j=i;j<=N;j+=i)prim[j]=1;}
			  }
    fout<<k;
}