N = int(input())
V = input().split()
dish_Array = []
count = 0
Array = [ [int(V[i]),i] for i in range(N)]
Array.sort(key = lambda Array: Array[0], reverse = True)
for i in range(N):
    if(Array[i][1] + 1 in dish_Array or Array[i][1] - 1 in dish_Array):
        continue
    count += Array[i][0]
    dish_Array.append(Array[i][1])
print(count)