#include <fstream>

using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");

const int nmax = 2000000;
bool ciur[nmax + 5];
int main()
{
    int i, n, j;
    ciur[1] = ciur[0] = 1;
    for ( i  = 2; i * i<= nmax; ++i )
        if ( ciur[i] == 0 )
            for ( j = i * i; j <= nmax; j += i )
                ciur[j] = 1;

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

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