import math
N=int(input())
LR=[]
D=[]
for _ in range(N):
    L,R=map(int,input().split())
    LR.append((L,R))
    D.append(L)
    D.append(R)
D.sort()
C=[0 for _ in range(len(D)-1)]
for L,R in LR:
    for i in range(D.index(L),D.index(R)):
        C[i]+=1
ans=0
for c in C:
    if c>=2:ans+=math.factorial(c)
print(ans+1)