#include <iostream>
#include <cstdio>
#include<cmath>
#define nmax 2000007
FILE * f=fopen("ciur.in","r");
FILE * g=fopen("ciur.out","w");
using namespace std;
int n;
char v[nmax];
int main()
{  int i,j,nr=0;

    fscanf(f,"%d",&n);
  for(i=2;i<=nmax;i++)
  {
      v[i]=1;
  }
  for(i=2;i<=n;i++)
    if(v[i])
   {
   nr++;
    for(j=2;j*i<=n;j++)
    v[i*j]=0;
   }
    int ok=1;

  fprintf(g,"%d",nr);
    return 0;
}