package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReaderSize(os.Stdin, 1<<20)

	var n int
	fmt.Fscan(in, &n)

	a := make([]int64, n)
	for i := 0; i < n; i++ {
		fmt.Fscan(in, &a[i])
	}

	var solve func(int, int, int64) int64
	solve = func(l, r int, base int64) int64 {
		if l > r {
			return 0
		}
		width := int64(r - l + 1)
		mn := a[l]
		for i := l + 1; i <= r; i++ {
			if a[i] < mn {
				mn = a[i]
			}
		}
		if mn-base >= width {
			return width
		}
		cost := mn - base
		i := l
		for i <= r {
			if a[i] == mn {
				i++
				continue
			}
			j := i
			for j <= r && a[j] > mn {
				j++
			}
			cost += solve(i, j-1, mn)
			if cost >= width {
				return width
			}
			i = j
		}
		if cost < width {
			return cost
		}
		return width
	}

	var ans int64
	i := 0
	for i < n {
		for i < n && a[i] == 0 {
			i++
		}
		if i == n {
			break
		}
		j := i
		for j < n && a[j] > 0 {
			j++
		}
		ans += solve(i, j-1, 0)
		i = j
	}

	fmt.Println(ans)
}