 #include<iostream>
 #include<stdio.h>
 #include<string>
 #include<math.h>
 #include<iomanip>
 #include<algorithm>
 #include<string.h>
 #include<cctype>
 #include<map>
 #include<set>
 #include<vector>
 #include<sstream>
 
 using namespace std;
 
 int arr[1000005]={0};
 
 bool isPrime(int x)
 {
   for(int i=3;i<=(int)(sqrt(x));i=i+2) 
   {
     if(x%i==0) return false;        
   }    
   return true;
 }
 
 int main()
 {
   int n;
   while(cin>>n)
   {
      if(n==1) cout<<"0"<<endl;
      else if(n==2) cout<<"1"<<endl;
      else if(arr[n]!=0) cout<<arr[n]<<endl;
      else
      {
        int count=1;
        for(int i=3;i<=n;i++)
        { 
          if(isPrime(i))
          { 
            count++;
            arr[i]=count;
          }
        }
        cout<<count<<endl;
      } 
   }
   //while(1);      
   return 0;    
 }
 