n = int(input()); mod = 998244353
bc = [tuple(map(int,input().split())) for _ in range(n)]
itov = set()
for b,c in bc: itov.add(b); itov.add(c+1)
itov = sorted(itov); m = len(itov)
vtoi = {v:i+1 for i,v in enumerate(itov)}
imos1 = [0]*(m+1); imos2=  [0]*(m+1)
for b,c in bc:
    rev1 = pow(c-b+1,mod-2,mod); rev2 = rev1**2%mod
    imos1[vtoi[b]] += rev1; imos2[vtoi[b]] += rev2
    imos1[vtoi[c+1]] -= rev1; imos2[vtoi[c+1]] -= rev2
for i in range(m):
    imos1[i+1] = sum(imos1[i:i+2])%mod
    imos2[i+1] = sum(imos2[i:i+2])%mod
two = pow(2,mod-2,mod); ans = n*(n-1)//2
for i in range(1,m): ans = (ans-(imos1[i]**2-imos2[i])%mod*two%mod*(itov[i]-itov[i-1]))%mod
for i in range(3,n+1): ans = ans*i%mod
print(ans)