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Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13
import sys

inN = int(sys.stdin.readline())

out = 1
for i in range(1,inN):
    out += i*12
sys.stdout.write(str(out))
