# A0, B0にはmin and maxがある

N = int(input())
A, B = [], []
for i in range(N-1):
    a, b = map(int, input().split())
    A.append(a)
    B.append(b)
sumA = sum(A)
sumB = sum(B)

A0_max = sumB
A0_min = 0
for i in range(N-1):
    calc = B[i]-(sumA-A[i])
    A0_min = max(A0_min, calc)

#print('A0_min', A0_min, 'A0_max', A0_max)

B0_max = sumA
B0_min = 0
for i in range(N-1):
    calc = A[i]-(sumB-B[i])
    B0_min = max(B0_min, calc)

#print('B0_min', B0_min, 'B0_max', B0_max)

diff = sumA-sumB
mn = max(A0_min, B0_min-diff)
mx = min(A0_max, B0_max-diff)
ans = max(mx+1-mn, 0)
print(ans)

#print('mn', mn, 'mx', mx)