import re
import sys

content = input()
pattern = r'^(\d+)$'
result = re.match(pattern, content)

if not result:
    sys.exit("format error.")

T = int(content)

if not (1 <= T and T <= 10**5):
    sys.exit("T")

S = []
for _ in range(T):
    content = input()
    pattern = r'^(\d+) (\d+)$'
    result = re.match(pattern, content)

    if not result:
        sys.exit("format error.")

    L, R = map(int, content.split())

    if not (2 <= L and L <= R and R <= 2 * 10**5):
        sys.exit("L, R")

print("OK")