'''
> https://www.codingame.com/ide/puzzle/organic-compounds
@author: olivier.massot, 2019
'''
import re

compounds = [re.findall("\(\d\)|CH\d|0", input().replace("   ", "0")) for i in range(int(input()))]
values = [[int(re.search(r"\d", c)[0]) for c in row] for row in compounds]

def getval(x, y):
    return values[y][x] if 0 <= y < len(values) and 0 <= x < len(values[y]) else 0
    
valid = all((sum([getval(x, y), getval(x - 1, y), getval(x + 1, y), getval(x, y - 1), getval(x, y + 1)]) == 4 \
             for y, row in enumerate(compounds) for x, v in enumerate(row) if v[0] == 'C'))
    
print("VALID" if valid else "INVALID")