N = int(input())
A = [0]*(N - 1)
B = [0]*(N - 1)
for i in range(N - 1):
    A[i], B[i] = map(int, input().split())

sumA = sum(A)
sumB = sum(B)

# 下限値を調べる
minA0, minB0 = 0, 0

for i in range(N - 1):
    memo = A[i] + B[i] - sumB
    minB0 = max(minB0, memo)

    memo = A[i] + B[i] - sumA
    minA0 = max(minA0, memo)

ans = 0
for a in range(minA0, sumB + 1):
    b = a + sumA - sumB
    if minB0 <= b <= sumA:
        ans += 1
print(ans)