from collections import Counter
n = int(input())
pairs = [(int(x[0]), int(x[1])) for x in [input().split() for _ in range(n)]]
xs, ys = [x for x, y in pairs], [y for x, y in pairs]
goal = max(xs) + min(xs), max(ys) + min(ys)
if n % 2: 
    print("impossible")
else:
    c = Counter(pairs)
    for p in c:
        if ((p[0]*2, p[1]*2) == goal and c[p] % 2) or (c[p] != c[(goal[0] - p[0], goal[1] - p[1])]):
            print("impossible")
            break
    else:
        print("possible")