import copy
N = int(input())
A = []
B = []
for i in range(N-1):
    a,b = map(int,input().split())
    A.append(a)
    B.append(b)
ma = max(sum(A),sum(B))

amarib = 0
D = copy.deepcopy(A)
for i in range(len(A)):
    b = B[i]
    for j in reversed(range(len(A))):
        if i==j:
            continue
        temp = min(D[j],b)
        b-=temp
        D[j]-=temp
    amarib += b

amaria = 0
D = copy.deepcopy(B)
for i in range(len(A)):
    a = A[i]
    for j in reversed(range(len(A))):
        if i==j:
            continue
        temp = min(D[j],a)
        a-=temp
        D[j]-=temp
    amaria += a
print(ma-max(amaria,amarib)+1)