x=eval(input())
a=[]
b=[]
c=[]
space=0
for i in range(x):
    y=[int(n) for n in input().split()]
    a.append(y)

for i in range(x):
    b.append(a[i][0])
b.sort()
for i in b:
    for j in range(x):
        if i==a[j][0]:
            m=j
            c.append(a[j])
    a.pop(m)
    x-=1
low=c[0][0]
high=c[0][1]
for i in c:
    if i[0]>=high:
        space+=(high-low)
        low=i[0]
        high=i[1]
    elif i[0]>=low and i[1]<=high:
        continue
    else:
        high=i[1]
space+=(high-low)
print(space)