n = int(input()) #waiting_for_pudging
b = list(map(int, input().split())) #waiting_for_pudging
summ = b[0] #waiting_for_pudging

for i in range(1, len(b)): #pudging
    summ += min(b[i-1], b[i]) #pudging
print(summ + b[-1]) #pugding
#accepted
