import std.algorithm, std.array, std.container, std.range;
import std.string, std.conv, std.math, std.random;
import std.stdio, std.typecons;

void main()
{
  auto n = readln.chomp.to!int;
  auto ai = readln.split.map!(to!int);

  auto min = int.max;
  auto sum = ai.sum;
  for (auto m = 1; m * m <= sum; ++m) {
    auto b = ai
      .zip(iota(n))
      .map!(a => a[0] - blocks(m, a[1]))
      .filter!(a => a < 0)
      .sum * (-1);
    if (ai.length < m * 2 - 1) {
      auto c = (m * 2 - 1) - ai.length;
      b += c * (c + 1) / 2;
    }
    auto r = sum - m * m + b;
    if (r < min) min = r;
  }

  writeln(min);
}

int blocks(int m, int i)
{
  if (i < m)
    return i + 1;
  else if (i >= m && i < m * 2 - 1)
    return m * 2 - i - 1;
  else
    return 0;
}