c_position = 1
iterations = 0
difference = 0


def minimilize(cposition, iters):
    temp = 0
    while cposition < l:
        if nums[cposition] < nums[cposition - 1]:
            temp += nums[cposition - 1] - nums[cposition]
        else:
            break
        cposition += 1
    return temp, cposition


def maximilize(cposition, iters):
    temp = 1
    while cposition < l:
        if nums[cposition] > nums[cposition - 1]:
            temp += nums[cposition] - nums[cposition - 1]
        else:
            break
        cposition += 1
    return temp, cposition


N = int(input())
nums = [int(item) for item in input().split()]
l = len(nums)

while c_position < l:
    if nums[c_position] < nums[c_position - 1]:
        results = minimilize(c_position, iterations)
        c_position = results[1]
        iterations += results[0]
        difference += results[0]
    elif nums[c_position] == nums[c_position - 1]:
        c_position += 1
    elif nums[c_position] > nums[c_position - 1]:
        results = maximilize(c_position, iterations)
        c_position = results[1]
        difference -= results[0]
    if difference < 0:
        iterations += abs(difference)
        difference = 0

print(iterations)