#include <fstream>
#include <cstring>
using namespace std;
 
ifstream fin("ciur.in");
ofstream fout("ciur.out");
 
int N;
bool prim[2000002];
int cnt;
 
int main()
{
    fin >> N;
    memset(prim, true, sizeof(prim));
    prim[0] = prim[1] = false;
    for ( int i = 2; i <= N; ++i )
        if ( prim[i] )
        {
            cnt++;
            for ( int j = 2 * i; j <= N; j = j + i )
                prim[j] = 0;
        }
 
    fout << cnt;
    return 0;
}