#include <iostream>
#include <vector>
#define LL long long
#define NMAX 2000005
#include <bitset>
#include <fstream>

using namespace std;
ifstream ciurin("ciur.in");
ofstream ciurout("ciur.out");
bitset <NMAX> isprime;
vector <int> pr;
int n,cont;
void ciur()
{
 for(LL i=2;i<=NMAX;i++){
    if(isprime[i]==0)
    {
        for(LL j=i*i;j<=NMAX;j+=i){
            isprime[j]=1;
        }
        pr.push_back(i);
    }
 }
}
int main()
{
    ciurin>>n;
    ciur();
    for(int i=0;pr[i]<=n;i++)
        cont++;
    ciurout<<cont;
    return 0;
}