#include<stdio.h>
FILE *f, *g;

bool a[2000000];
int main()
{ 
  f=fopen("ciur.in", "r");
  g=fopen("ciur.out", "w");
  int n, nr=0, i=2, j;
  fscanf(f, "%d", &n);
  for(i=2; i<=n; ++i) if(!a[i]) { ++nr;
						          for(j=i; j<=n; j+=i) a[j]=1; 
                                }
  fprintf(g, "%d", nr);
  fclose(f);
  fclose(g);
  return 0;
}