N = int(input())
AB = []
XA, XB = 0, 0
for i in range(N - 1):
    a, b = map(int, input().split())
    AB.append((a, b))
    XA += a
    XB += b
cnt = 0
for a0 in range(XB + 1):
    b0 = XA + a0 - XB
    if b0 < 0 or b0 > XA:
        continue
    for a, b in AB:
        if a > XB + b0 - b:
            break
    else:
        cnt += 1
print(cnt)