#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)
        numere[i] = 1;
    for (i = 2; i <= n; ++i)
        if (numere[i]==1)
        {
            ++prim;
            for (j = i+i; j <= n; j += i)
                numere[j] = 0;
        }
    g<<prim;
    return 0;
}