N = int(input())
Y = list(map(int,input().split()))

if N == 1:
    print(0)
    exit()
if N == 2:
    print(max(0, Y[0]-Y[1]))
    exit()

ans = 0
for i in range(N-2):
    if Y[i] <= Y[i+1] and Y[i+1] > Y[i+2]:
        to = max(Y[i], Y[i+2])
        ans += Y[i+1]-to
        ans += to-Y[i+2]
        Y[i+1] = Y[i+2] = to

print(ans)