The chalky smell of a black board is something that will always remind us of those long days spent sitting in our desks taking notes instead of playing outside. *If we think about it, life is just a mere blink of an eye in terms of time. But time is a relative thing.* sighed our math teacher as he approached a picture of the class picture we took at the beginning of the year. He stood there for a while glaring at the picture... then as usual, he strolled back to his desk and pulled out a shiny new math book. He flipped through the first couple of pages and suddenly stopped.*Let's see who can solve this one...*

You are given N number of points. Find a function of the format `f(x)=a*x+b`

for which `∑((y[i]-f(x[i]))^2)`

is minimal, where `x[i]`

and `y[i]`

are coordinates for the point `i`

.

## Input

`N`

, the number of points is on the first line. The next `N`

lines are occupied by pairs of numbers which represent the coordinates of each point. ## Output

On the first line will be the minimum cost, with 10^{-3}decimal precision, on the only line.

## Constraints

`1 ≤ N ≤ 1000`

`-100 000 ≤ x[i], y[i] ≤ 100 000`

The output result is considered correct if and only if the diference between your result and the correct one is less then or equal to 1e-3.

## Sample

Input | Output |
---|---|

9 60 136 69 198 66 194 64 140 54 93 67 172 59 116 65 174 63 145 | 1093.66860465 |

7 1975 30.663 1980 37.995 1985 42.815 1990 49.951 1995 54.177 2000 60.502 2005 65.199 | 3.50440143 |