A.cpp

/*****                                            
                                                     __Bismillahir Rahmanir Rahim__
                                               American International University Bangladesh (AIUB) 
                                                          Hadiur Rahman Nabil
                                                                 
                                                               
                                                          
*****/
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector <int> vi;

#define INF 1000000007

#define pb push_back
#define mp make_pair
#define endl "\n"

  
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    float a,b;
    float c,d;
    cin>>a>>b;
    d=(a-b)/3.00;
    c=d+b;
    cout<<c<<"\n";
   return 0;
}