n = int(input())
if n % 2: print("impossible"), exit()
t, a = n // 2, sorted(tuple(map(int, input().split())) for _ in range(n))  # `t` is the number of teams
# `goal` = `(b, p)` are the exact skill per team. In case any of them is fractional, "impossible" is printed.
goal = tuple(sum(skill_list) / t for skill_list in zip(*a))
print(("im" if any(tuple(sum(z) for z in zip(*tuples)) != goal for tuples in zip(a, a[::-1])) else "") + "possible")