#include<fstream>
#include<iostream>
#include<cstring>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];
int main()
{
     int n;
     in>>n;
     int q=1;
     while(q*q<=n)
     {
         q++;
        if(v[q]==0)
        for(int i=q*2;i<=n;i=i+q)
           v[i]=1;
     }
     int k=0;
     for(int i=2;i<=n;i++)
         if(v[i]==0)
            k++;
     out<<k;
}