#include <stdio.h>
#include <stdlib.h>

char ciur[2000001];

int main() {
    FILE *fin, *fout;
    int n, d, i;
    fin = fopen( "ciur.in", "r" );
    fout = fopen( "ciur.out", "w" );
    fscanf( fin, "%d", &n );
    for( d = 2; d * d <= n; d++ )
      if( ciur[d] == 0 )
        for( i = d * d; i <= n; i += d )
          ciur[i] = 1;
    d = 0;
    for( i = 2; i <= n; i++ )
      if( ciur[i] == 0 )
        d++;
    fprintf( fout, "%d", d );
    fclose( fin );
    fclose( fout );
    return 0;
}