N, M = map(int, input().split())
A = list(map(int, input().split()))
ans = N - M
now = A[0]
for i in range(1, M):
    tmp = (A[i] - now)
    tmp2 = 1
    while tmp % 2 == 0 and tmp > 3:
        tmp //= 2
        ans -= tmp2
        tmp2 *= 2
    now = A[i]
print(ans)