# A1, B1にはminimum to maxがある
# 入力例1
# A1 minは、たとえばB2-A3
# A1 maxは、B2+B3

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)
A1_min = 0
A1_max = sumB
B1_min = 0
B1_max = sumA

for i in range(N-1):
    A1_min = max(A1_min, B[i]-(sumA-A[i]))
    B1_min = max(B1_min, A[i]-(sumB-B[i]))

ans = 0
for a in range(A1_min, A1_max+1):
    b = sumA + a - sumB
    if B1_min <= b <= B1_max:
        ans += 1
        #print('a', a, 'b', b)
print(ans)