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


using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

bitset <Nmax> isprime;
vector <int>  pr;
int N;

void ciur()
{
    for(int LL i=2;i<=Nmax;i++)
    {
        if(isprime[i]==0)
        {
            for(int LL j=i*i;j<=Nmax;j+=i)
                isprime[j]=1;
        pr.push_back (i);
        }
    }
}


int main()
{
    int N,cont=0,i;
    fin>>N;
    ciur();
    for(i=0;pr[i]<=N;i++)
    {
        cont+=1;
    }

    fout<<cont;
    return 0;
}