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

cnt = 0
for i in range(sumA+sumB,max(sumA,sumB)-1,-1):
    f = True
    lsA1 = lsA[:]+[i-sumA]
    lsB1 = lsB[:]+[i-sumB]
    for j in range(N):
        if lsA1[j] > i-lsB1[j]:
            f = False
    if f:
        cnt += 1
print(cnt)