n, m = map(int, input().split())
A = list(map(int, input().split()))
ans = 0
for i in range(m - 1):
    d = A[i + 1] - A[i]
    ans += d - 1
    minus = 1
    while d % 2 == 0 and d > 2:
        d //= 2
        ans -= minus
        minus *= 2
print(ans)