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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
FIN = sys.stdin
FOUT = sys.stdout

a = int(FIN.readline())
ans = 1
for i in range(a):
    ans += 12 * i
    
FOUT.write(str(ans))