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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 math
import sys
input = sys.stdin.readline

def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))

n = inp()
print(n*(n-1)*6 + 1)