时间复杂度 $O(nlogn)$

n = int(input())
lt = [list(map(int, input().split(" "))) for _ in range(n)]
lt.sort()
res = []
maxR = l[0][1]
maxL = l[0][0]
for i in lt:
    l, r = i
    if maxR >= lt:
        maxR = max(r, maxR)
    else:
        res.append([maxL, maxR])
        maxL = l
        maxR = r
res.append([maxL, maxR])        
print(len(res))