N=int(input())
A=[];c=10**10
for i in range(N):
  l,r=map(int, input().split())
  A.append((l,r))
  
A=sorted(A,key=lambda x: x[1])
A=sorted(A,key=lambda x: x[0])
#print(A)
B=[]
ll=-10**10;rr=10**10
for i in range(N):
  l,r=A[i]
  ll=max(ll,l-i)
  rr=min(rr,r-i)
p,q=ll,rr#
#print(ll,rr)
  
A=sorted(A,key=lambda x: x[0])
A=sorted(A,key=lambda x: x[1])
#print(A)
ll=-10**10;rr=10**10
for i in range(N):
  l,r=A[i]
  ll=max(ll,l-i)
  rr=min(rr,r-i)
r,s=ll,rr
if r>s and p>q:
  print(0)
elif r>s:
  print(q-p+1)
elif p>q:
  print(s-r+1)
else:
  print(-1)