from sys import stdin
input = stdin.readline
tour = [input() for _ in range(36)]
board = [[0 for _ in range(6)] for _ in range(6)]
sx, sy = ord(tour[0][0]) - 65, int(tour[0][1]) - 1
board[sx][sy] = 1
flag = True
# 고려 사항 1
if abs(ord(tour[0][0]) - ord(tour[-1][0])) == 2 and abs(int(tour[0][1]) - int(tour[-1][1])) == 1 \
or abs(ord(tour[0][0]) - ord(tour[-1][0])) == 1 and abs(int(tour[0][1]) - int(tour[-1][1])) == 2:
for i in range(1, len(tour)):
nx, ny = ord(tour[i][0]) - 65, int(tour[i][1]) - 1
# 고려 사항 2
if abs(nx - sx) == 2 and abs(ny - sy) == 1 or abs(nx - sx) == 1 and abs(ny - sy) == 2:
board[nx][ny] += 1
# 고려 사항 3
if board[nx][ny] != 1:
flag = False
break
else:
flag = False
break
sx, sy = nx, ny
else:
flag = False
if flag:
print("Valid")
else:
print("Invalid")
※ 고려 사항
[2,1], [1,2]
를 만족하는가. (아니라면 처음 자리로 돌아오지 못함)[2,1], [1,2]
를 만족하는가. (아니라면 경로가 잘못되었음)