n,k=map(int,input().split())
a=map(int,input().split())
print(max(0,(n*(k*10-5)-sum(a)*10)//5))230B - T-primes | 630A - Again Twenty Five |
1234D - Distinct Characters Queries | 1183A - Nearest Interesting Number |
1009E - Intercity Travelling | 1637B - MEX and Array |
224A - Parallelepiped | 964A - Splits |
1615A - Closing The Gap | 4C - Registration System |
1321A - Contest for Robots | 1451A - Subtract or Divide |
1B - Spreadsheet | 1177A - Digits Sequence (Easy Edition) |
1579A - Casimir's String Solitaire | 287B - Pipeline |
510A - Fox And Snake | 1520B - Ordinary Numbers |
1624A - Plus One on the Subset | 350A - TL |
1487A - Arena | 1520D - Same Differences |
376A - Lever | 1305A - Kuroni and the Gifts |
1609A - Divide and Multiply | 149B - Martian Clock |
205A - Little Elephant and Rozdil | 1609B - William the Vigilant |
978B - File Name | 1426B - Symmetric Matrix |