#a = [1,2,3, 1, 3, 3, 6, 4, 2, 3, 5, 1, 0, 6, 7, 6, 7, 6, 3]
a = [1, 2, 5, 4]
res = 0
b = 0
for i in range(1, len(a)):
if a[i - 1] == a[i]:
b = 0
else:
sign = 1 if a[i - 1] < a[i] else -1
res += a[i] * sign
if b != sign:
res += a[i - 1] * sign
b = sign
print(res) # -1