#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
bool v[2000050];
int n,i,j,cn;
int main()
{
    f>>n;
    int cn;
    cn=0;
    for(i=2;i*i<=n;i++)
    {if(v[i]==1)
         continue;
       for(j=i*2;j<=n;j=j+i)
           {
             v[j]=1;
           }
    }
         for(i=2;i<=n;i++)
            if(v[i]==0)cn++;
      g<<cn;
}