import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

N = int(readline())
m = map(int,read().split())
A,B = zip(*zip(m,m))

A,B

SA = sum(A)
SB = sum(B)

low = max(SA,SB,max(a+b for a,b in zip(A,B)))
high = SA + SB

answer = high - low + 1
if answer < 0:
    answer = 0
print(answer)