N,M = map(int,input().split())
board = []
for _ in range(M):
    a,b = map(int,input().split())
    board.append((a,b))
board.sort(key=lambda x:x[1])
cnt = 0
lastr = 0
for l,r in board:
    if lastr <= l:
        cnt += 1
        lastr = r
ans = 2 * (N-1) -cnt
print(ans)