N, M = map(int, input().split())
A = list(map(int, input().split()))
ans = 0

def f(x):
    if x % 2 == 0 or x == 1:
        return 0
    return 2 * f(x//2) + 1

for i in range(M - 1):
    ans += f(A[i + 1] - A[i] - 1)
print(N - M - ans)