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

const int nmax = 2000000;
bitset <2000001> ciur;

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

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

    cout << cnt << endl;

   // for ( i = 1; i <= 20;++i )
       // cout << ciur[i] << " ";


    return 0;
}