n = int(input())
a = [int(s) for s in input().split()]
b = a.copy()
max_index = a.index(max(a))
count = 0
last_index = len(a)
while(last_index > 0):
    b[max_index: last_index] = [a[max_index]] * (last_index - max_index)
    last_index = max_index
    
    if last_index == 0 or len(set(a[:last_index])) <= 1:
        break
    max_index = a.index(max(a[:last_index]))

for i in range(len(a)):
    count += b[i] - a[i]
print(count)