n = int(input())
ab = [[int(i) for i in input().split()] for j in range(n-1)]

a = 0
b = 0
for i in range(n-1):
    A,B = ab[i]
    a += A
    b += B

mx = [a,b]
ab.sort(key=lambda x:(-x[0],-x[1]))

cnt = 0

for i in range(n-1):
    a,b = ab[i]
    for j in range(n-2):
        tmp = min(a,ab[(i+j+1)%(n-1)][1])
        a -= tmp
        ab[(i+j+1)%(n-1)][1] -= tmp
        cnt += tmp
        if a == 0:
            break
    #print(cnt,i)
print(cnt+1)