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


   ifstream in("ciur.in");

   ofstream out("ciur.out");
   cin>>n;


   v[0]=v[1]=1;
    for(i=2;i*i<=n;i++)
    if(v[i]==0)
    {
        for(j=i*i;j<=n;j+=i)
        v[j]=1;
    }
for(i=2;i<n;i++)
if(v[i]!=0)
    s++;
cout<<s;


    return 0;
}