N = int(input())
Y = [int(zz) for zz in input().split()]


ans = 0
for i in range(1,N):
    if Y[i] < Y[i-1]:
        left = 0
        for j in range(i):
            left += max(Y[j]-Y[i],0)
        right = 0
        for j in range(i,N):
            right += max(Y[i]-Y[j],0)

        if left < right:
            ans += Y[i-1]-Y[i]
            Y[i-1] = Y[i]
        else:
            ans += Y[i-1]-Y[i]
            Y[i] = Y[i-1]
print(ans)