def split(l, r):
    ans = 0
    left = l
    for i in range(l, r):
        if d[i] == 0:
            ans += fill(left, i)
            left = i + 1
    ans += fill(left, r)
    return ans


def fill(l, r):
    if l >= r:
        return 0
    if l == r - 1:
        return d[l]
    for i in range(l, r):
        d[i] -= 1
    return 1 + split(l, r)


n = int(input())
m = input()
d = []
for i in m.split():
    d.append(int(i))
print(split(0, n))