#include <stdio.h>
#include <fstream>
#include <iostream>
using namespace std;
char v[2000005];
long long x,s,a,i,j,n;
int main()
{
   //cout<<sizeof(v[2000005]);


   ifstream in("ciur.in");

   ofstream out("ciur.out");
   v[0]=v[1]=1;
    for(i=2;i*i<=2000000;i++)
    {
        for(j=i*2;j<=2000000;j+=i)
        v[j]=1;

    }
    cin>>n;
for(i=2;i<n;i++)
if(v[i]!=0)
s++;
cout<<s;




    return 0;
}