#include <iostream>
#include <fstream>
#define LL long long
#define NMAX 2000005
#include <vector>
#include <bitset>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,cont,a;
bitset <NMAX> isprime;
vector <int> pr;
void ciur()
{
    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()
{
    f>>n;
    ciur();
    for(a=0;pr[a]<=n;a++)
        cont++;
    g<<cont;
    return 0;
}