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n = int(input()) s = 0 l = 30001 for i in range(n): a, b = map(int, input().split()) s += min(a, b) if abs(a-b) < l and abs(a-b) % 4 != 0: l = abs(a-b) if s % 4 == 0: s += l if l == 30001: print("no") else: print(s) else: print(s)