#include<iostream>
#include<cstdio>
using namespace std;

int main(){
   int i,j,n,flag=0,x=1;
   int sosu[999];
   sosu[0] = 2;
   cin>>n;
   for(i=3;i<=n;i++){
      flag = 0;
      
      for(j=0;j<x;j++){
         if(i%sosu[j] == 0){
            flag++;
            break;
         }
      }
      if(flag == 0){
         sosu[x] = i;
         x++;
      }
   }
   printf("%d\n",x);
   return 0;
}