N = int(input())
L = [[int(l) for l in input().split()] for _ in range(N-1)]

A = 0
B = 0
for t in L:
    A += t[0]
    B += t[1]

ans = 0
for i in range(B+1):
    j = A+i-B
    if j < 0:
        continue
    flag = True
    for t in L:
        if t[0] > B+j-t[1]:
            flag = False
            break
    if flag:
        ans += 1
print(ans)