#include <fstream.h>

int a[2000000], i, j, n, nr = 0;

int main()
{
    ifstream fin("ciur.in");
    fin >> n;
    fin.close();
    ofstream fout("ciur.out");
    for ( i = 0; i < n; i++)
    	a[i] = 1;
   	for ( i = 2; i * i <= n; i++)
   		if ( a[i] )
   		{
   		    j = 2;
   		    while ( i*j < n )
   		    {
   		        a[i*j] = 0;
   		        j++;
	        }
        }
    for ( i = 2; i <= n; i++)
    	if ( a[i] )
    	nr++;
     fout << nr;
     fout.close();
      return 0;
}