除第8得分点外全部WA

n=int(input())
beg=[]
end=[]
for i in range (n):
    a,b=map(int,input().split(' '))
    beg.append(a)
    end.append(b)
sum=0
for i in range (0,n):
    beg1=beg[:]
    end1=end[:]
    beg1.pop(i)
    end1.pop(i)
    beg1.sort()
    end1.sort()
    if(end1[-1]-beg1[0]>sum):
        sum=end1[-1]-beg1[0]
print(sum)