#include <iostream>
#include <fstream>
#define DIM 1000000
using namespace std;
ifstream fin("date.in");
ofstream fout("date.out");

int e[DIM];

long long er(long long n)
{
    int nr=0;
    for (int i=2;i<=n;i++)
    {
        if (e[i]==0)
        {
            nr++;
            for (int j=i*2;j<=n;j+=i)
                e[j]=1;
        }
    }
    return nr;
}

int main()
{
   long long n;
   fin>>n;
   fout<<er(n);
}