[백준][Python] 1931번 회의실 배정

n = int(input())
time = []
for i in range(n):
    start_time,end_time = map(int,input().split())
    time.append((start_time,end_time))
time = sorted(time,key=lambda x : (x[1],x[0]))
before_end_time = 0
count = 0
for start_time,end_time in time:
    
    if start_time >= before_end_time:
        count +=1
        before_end_time = end_time

print(count)