#include <fstream>
#define InFile  "ciur.in"
#define OutFile "ciur.out"
#define MAX 2000001

using namespace std;

ifstream fin  (InFile);
ofstream fout (OutFile);

unsigned int N;

bool c[MAX];
unsigned int i, j;

unsigned int sol;

int main ()
{
    fin >> N;
    for (i=2; i<=N; i++)
        if (c[i] == 0)
        {
            sol++;
            for (j=2*i; j<=N; j+=i)
                c[j] = 1;
        }
    fout << sol;
    return 0;
}