#include <stdio.h>

int main()
{
    FILE *fin, *fout;
    int n, prime, div, j;
    char ciur[2000000];

    fin = fopen ( "ciur.in", "r" );
    fout = fopen ( "ciur.out", "w" );
    fscanf ( fin, "%d", &n );
    fclose ( fin );

    prime = 0;
    for ( div = 2; div < n; div++ ) {
      if ( ciur[div] == 0 ) {
        prime++;
        for ( j = div + div; j <= n; j = j + div ) {
          ciur[j] = 1;
        }
      }
    }

    fprintf( fout, "%d", prime );
    fclose ( fout );

    return 0;
}