#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

#define NMAX 2000001
int A[NMAX],N,i,j;
int nrPrime = 0;

int main()
{
    int N;

    f >> N;
    for(i=2; i<=N; i++)
        A[i] = 1;

    for(i=3; i<=N; i++)
    {
        if(A[i] == 1)
        {
            nrPrime++;
            for(int j=i+i; j<=N; j+=i)
                A[j] = 0;
        }
    }

    g << nrPrime;

    return 0;
}