python3解法
n = int(input())
segs = []
for i in range(n):
segs.append(list(map(int, input().split())))
# print(segs)
res = []
segs.sort()
# print(segs)
st = float("-inf")
ed = float("-inf")
for l, r in segs:
# print(l)
if ed < l:
if st != float("-inf"):
res.append((st, ed))
st = l
ed = r
else:
ed = max(ed, r)
if st != float("-inf"):
res.append((st, ed))
print(len(res))