#!/usr/bin/env python3

lo = []
hi = []

def compatible( i:int, j:int ) -> bool:
    return lo[i]<=j and j<=hi[i] and lo[j]<=i and i<=hi[j]

assigned = []
n = int( input().strip() )
for _ in range(n):
    a, b = [int(x)-1 for x in input().strip().split()]
    lo.append(a)
    hi.append(b)
    assigned.append(False)

count = 0
for i in range(n):
    if not assigned[i]:
        for j in range(i+1,n):
            if assigned[i]: break
            if not assigned[j] and compatible(i,j):
                for k in range(j+1,n):
                    if assigned[i] or assigned[j]: break
                    if not assigned[k] and compatible(i,k) and compatible(j,k):
                        assigned[i] = True
                        assigned[j] = True
                        assigned[k] = True
                        count += 1

print(count)