#include <iostream>

#define NMax 2000005

using namespace std;

int N, NPrime;
bool V[NMax];

void Eratosthenes ()
{
    for (int i=2; i<=N; ++i)
    {
        if (!V[i])
        {
            ++NPrime;
            for (int j=i+i; j<=N; j+=i)
            {
                V[j]=true;
            }
        }
    }
}

int main()
{
    freopen ("ciur.in", "r", stdin);
    freopen ("ciur.out", "w", stdout);
    scanf ("%d", &N);
    Eratosthenes ();
    printf ("%d\n", NPrime);
    return 0;
}