import sys
input = sys.stdin.readline

n, m = map(int, input().split())
edges = [[x - 1 for x in map(int, input().split())] for _ in [0] * m]

plans = sorted(edges, key=lambda x : x[1])
now = 0
ans = 2 * (n - 1)
for x, y in plans:
    if(now > x):
        continue
    now = y
    ans -= 1
print(ans)