Wężyk

Staś's favorite game is called wężyk (a little snake). First he chooses one integer $n$, then he starts writing consecutive natural numbers on a sheet of paper. In total he writes $n$ rows, each containing $n$ numbers.

In the first row Staś writes the numbers from $1$ to $n$ from left to right. The second row, however, he fills from right to left with the numbers from $n + 1$ to $2n$. And so on: odd-numbered rows are filled from left to right, and even-numbered rows from right to left.

Your task is to write a program that plays wężyk automatically.

The first and only line of input contains one natural number $n$ ($1 \le n \le 100$).

Print $n$ rows, each containing $n$ natural numbers. In total $n^2$ numbers must be printed: all natural numbers from $1$ to $n^2$. Within each row the numbers must be separated by single spaces.