#include <stdio.h>

char ciur[2000001];

int main(){
    int n, s;
    FILE *fin, *fout;

    fin = fopen( "ciur.in", "r" );
    fscanf( fin, "%d", &n );
    fclose( fin );
    s = 0;

    for ( int i = 2; i * i <= n; i++ ) {
      if ( ciur[i] == 0 )
        for ( int d = i * i; d <= n; d = d + i )
          ciur[d] = 1;
    }
    for ( int i = 2; i <= n; i++ )
      if ( ciur[i] == 0 )
        s++;
    fout = fopen( "ciur.out", "w" );
    fprintf( fout, "%d", s );
    fclose( fout );

    return 0;
}