A. Already 2018 … String concatenation and slicing
print('2018'+input()[4:])
B. Kagami Mochi … I used set. As all values added into the set is unique(duplicated values will be ignored), I just need to output the numbers of the set once all input is completed.
s = set() for _ in range(int(input())): s.add(input()) print(len(s))
C. Otoshidama … I used simple two for loops to iterate the numbers of 10,000 notes and 5,000 notes. Hence the cost is N^2.
def otoshidama(nos, amt): for x in range(0, amt//10000+1): for y in range(0, (amt-(10000*x))//5000+1): if 10000*x + 5000*y + 1000*(nos-x-y) == amt: return (x, y, nos-x-y) return (-1, -1, -1) n, y = list(map(int,input().split())) print(*otoshidama(n, y))