package main

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

var sc = bufio.NewScanner(os.Stdin)
var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func main() {
	sc.Split(bufio.ScanWords)
	n := nextInt()
	ns, sum := make([]int, n), 0
	for i := range ns {
		c := nextInt()
		sum += c
		ns[i] = c
	}

	h := 0
	for i := 1; ; i++ {
		if i*i > sum {
			h = i - 1
			if h*2-1 > len(ns) {
				h = n/2 + 1
			}
			break
		}
	}

	count := h - ns[h-1]
	for i := 0; i < h-1; i++ {
		count += (i + 1) - ns[i]
		count += (h - 1 - i) - ns[i+h]
	}

	for _, v := range ns[h*2-1:] {
		count += v
	}
	fmt.Println(count)
}

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	i, _ := strconv.Atoi(nextLine())
	return i
}