#include <fstream>
#define NMAX 2000010
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
    int n,prim=0,i,j;
    char numere[NMAX];
    f>>n;
    for (i=2;i<=n;++i)
        if (!numere[i])
        {
            ++prim;
            for (j=i+i;j<=n;j+=i)
                numere[j]=1;
        }
    g<<prim;
    return 0;
}