#include <fstream>
#include <cstring>
#define NMAX 2000001

using namespace std;

long N , cnt = 0;
bool prim[NMAX]; /// ne-prim initial

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin >> N;
    memset( prim , true , sizeof( prim ) );
    for ( long i = 2 ; i <= N ; ++i )
        if ( prim[i] )
        {
            ++cnt;
            for ( long j = i + i ; j <= N ; j += i )
                prim[j] = 0;
        }
    fout << cnt;
    return 0;
}