class p:
    def __init__(self,l,r):
        self.l=l
        self.r=r
    def __lt__(self,b):
        if(self.l==b.l):
            return self.r<b.r
        else:
            return self.l<b.l

l=[p(0,0) for i in range(1001000)]
n=int(input())
for i in range(1,n+1,1):
    a,b=map(int,input().split())
    l[i].l=a
    l[i].r=b
sorted(l)
L=l[1].l
R=l[1].r
ans=0
for i in range(2,n+1,1):
    if R>=l[i].l:
        R=max(R,l[i].r)
    else:
        ans+=R-L+1
        L=l[i].l
        R=l[i].r
print(ans+R-L+1)