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)