#include <iostream>
#include <fstream>
#define NMAX 2000005
#define LL long long
#include<vector>
#include<bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset <NMAX> isprime;
vector <int> pr;
int n, cont;
 void ciur()
{   int n;
    for(LL i=2;i<=NMAX;i++)
        {
            if(isprime[i]==0)
            {
                for(LL j=i*i;j<=NMAX;j=j+i)
                    isprime[j]=1;
                pr.push_back(i);
            }

        }
}

 int main()
 {
     fin>>n;
     ciur();
     for(int i=0; pr[i] <= n; i++)
     {
         cont++;
     }
     fout << cont;
    return 0;
 }