#include <iostream>
#include <fstream>
#include <cstdio>
using namespace std;
ofstream g("ciur.out");
unsigned char a[1000005];
int j,i,n,k;
int main()
{
    freopen("ciur.in","r",stdin);
    scanf("%d",&n);
    for(i=1;i*i<=n/2;i++)
    {
        if(a[i]==0)
        {
            for(j=3*i+1;j<=n/2;j=j+2*i+1)
                a[j]=2;
      }
    }
    i=1;
    for(k=1;k<=n/2;k++)
    {
        if(a[k]==0)
        {
            if(2*k+1<=n)
            {
             i++;
            }
        }
    }
    g<<i<<'\n';
    return 0;
}