n = int(input())
A = list(map(int, input().split()))
pre = A[0]
cnt = 0
kaisa = [0] * (n - 1)
for i in range(n - 1):
    kaisa[i] = A[i + 1] - A[i]
for i in range(n - 1):
    if kaisa[i] >= 0:
        continue
    if i >= 1:
        if kaisa[i - 1] > 0:
            cnt += min(kaisa[i - 1], -kaisa[i])
            kaisa[i] = min(kaisa[i] + kaisa[i - 1], 0)
            if kaisa[i] >= 0:
                continue
    cnt += -kaisa[i]
    if i != n - 2:
        kaisa[i + 1] += kaisa[i]


print(cnt)