#include <cstdio>
#include <bitset>
using namespace std;
int const NM = 2e6 + 7;
bitset <NM> v;
char const in [] = "ciur.in";
char const out [] = "ciur.out";
int best;
void ciur (int n)
{
    int i , j;
    for(i = 2 ; i * i <= n ; ++ i)
        if(! v [i])
            for(j = i * i ; j <= n ; j += i)
                v [j] = 1;
    for(i = 2 ; i <= n ; ++ i)
        if(! v [i])
            ++ best;
    printf ("%d" , best);
    puts("");
}
int main()
{
    freopen (in , "r" , stdin);
    freopen (out , "w" , stdout);
    int n , i , best = 0;
    scanf ("%d", &n);
    ciur (n);
    return 0;
}