r=input;w,u=map(int,r().split());d=[0]*(w+1)
for _ in range(w-1):a,b=map(int,r().split());d[a]+=1;d[b]+=1
print(2*u/sum(1 for j in d if j==1))
426A - Sereja and Mugs | 363A - Soroban |
1585C - Minimize Distance | 1506E - Restoring the Permutation |
1539A - Contest Start | 363D - Renting Bikes |
1198D - Rectangle Painting 1 | 1023B - Pair of Toys |
1725A - Accumulation of Dominoes | 1675E - Replace With the Previous Minimize |
839A - Arya and Bran | 16B - Burglar and Matches |
1625B - Elementary Particles | 1725G - Garage |
1725B - Basketball Together | 735A - Ostap and Grasshopper |
1183B - Equalize Prices | 1481A - Space Navigation |
1437B - Reverse Binary Strings | 1362B - Johnny and His Hobbies |
1299A - Anu Has a Function | 1111A - Superhero Transformation |
954A - Diagonal Walking | 39F - Pacifist frogs |
1451C - String Equality | 386A - Second-Price Auction |
1690E - Price Maximization | 282B - Painting Eggs |
440A - Forgotten Episode | 233B - Non-square Equation |