## https://yukicoder.me/problems/no/1995

import math

def main():
    N, M = map(int, input().split())
    ab = []
    b_map = {}
    for _ in range(M):
        a, b = map(int ,input().split())
        ab.append((a ,b))
        if b not in b_map:
            b_map[b] = []
        b_map[b].append(a)
    
    pos_set = set()
    for a, b in ab:
        pos_set.add(a)
        pos_set.add(b)
    pos_set.add(1)
    pos_set.add(N)
    pos_list = list(pos_set)
    pos_list.sort()

    answer = 0
    dp = {1: 0}
    for i in range(len(pos_list)):
        p = pos_list[i]

        ans = answer
        if p in b_map:
            for q in b_map[p]:
                ans = max(ans, dp[q] + 1)
        dp[p] = ans
        answer = ans
    
    x = dp[N]
    answer = 2 * (N - 1) - x
    print(answer)








    



if __name__ == "__main__":
    main()