#!/usr/bin/env python3
p, ok = sorted(list(tuple(map(int, input().split())) for _ in range(int(input())))), True
for a, b in zip(p, reversed(p)):
    if (a[0]+b[0], a[1]+b[1]) != (p[0][0] + p[-1][0], p[0][1] + p[-1][1]):
        ok = False
print('possible' if len(p)%2==0 and ok else 'impossible')