def isin(a, b):
    if b >= a[0] and b <= a[1]:
        return 1
    else:
        return 0


def choose(x, l):
    s = 0
    chose = []
    for i in x:
        for j in range(len(l)):
            s = s + isin(l[j], i)
        chose.append(s)
        s = 0
    index = chose.index(max(chose))
    num = x[index]
    new = []

    for j in range(len(l)):
        if not isin(l[j], num):
            new.append(l[j])
    return new


n = int(input())
l = []
total=[]
for i in range(n):
    x = list(map(int, input().split()))
    for i in range(x[0],x[1]+1):
        total.append(i)
    l.append(x)
k = 0
while len(l) > 0:
    l = choose(total, l)
    k = k + 1
print(k-1)