12

p = 0
if len(a) > 1:
    for i in range(n):
        if i == 0:
            p+=a[i]+abs(a[i]-a[i+1])
        elif i>0 and i<n-1:
            p+=abs(a[i]-a[i+1])
        else:
            p+=a[n-1]
    print(n*2+p)
else:
    print(2+2*a[0])