#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int d,n,j,i,nr;
char ciur[2000005];
int main()
{
    fin>>n;

    for (i = 2; i <= n; ++i)
        if (ciur[i]==0)
        {
            ++nr;
            for (j = i+i; j <= n; j += i)
                ciur[j] = 1;
        }
    fout<<nr;
    return 0;
}