n = int(input())
h = list(map(int, input().split()))
a = 0

if h[0] == 0:
    a += h[1]
if h[-1] == 0:
    a += h[-2]
for i in range(1, n-1):
    if h[i] == 0:
        a += min(h[i-1], h[i+1])

print(a)