#include <fstream>
#include <bitset>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");

const int nmax = 2000000;
bitset <1000001> ciur;
int main()
{
    int i, n, j;
    ciur[0] = 1;
    for ( i  = 3; i * i <= nmax; i += 2 )
        if ( ciur[i / 2] == 0 )
            for ( j = i * i; j <= nmax; j += 2 * i )
                ciur[j / 2] = 1;

    cin >> n;
    int cnt = 1;
    for ( i = 2; i <= n; ++i )
        if ( ciur[i / 2] == 0 && i % 2 == 1 )
            ++cnt;

    cout << cnt << endl;
    return 0;
}