N = int(input())
AB = [list(map(int,input().split())) for i in range(N-1)]

s = 0
t = 0
for i in range(N-1) :
    s += AB[i][1]
    t += AB[i][0]

u = t-s

if u < 0 :
    print(s + u + 1)
else :
    print(s+1)