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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
n=int(input())
if n==1:
    print(1)
else:
    s=0
    for i in range(n):
        s+=12*i
    s+=1
    print(s)