#include <fstream>
#include <math.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int v[2000005];
void ciur()
{
    int n=2000005;
    int lim,i,j;
    lim=(int)sqrt((double)n);
    for(i=4;i<=n;i=i+2)
        v[i]=1;
    for(i=3;i<=lim;i=i+2)
    {
        if(v[i]==0)
         {
           for(j=i*i;j<=n;j=j+(i*2))
               v[j]=1;
         }
    }
}
int main()
{
    int n,sol,i;
    ciur();
    sol=1;
    fin>>n;
    for(i=3;i<=n;i+=2)
        if(v[i]==0)
           sol++;
    fout<<sol<<"\n";
    fin.close();
    fout.close();
    return 0;
}