题解 | #等差数列#

def get_ans(s):
    li=[i for i in range(2,2+(s-1)*3+1,3)]
    return sum(li[:s])

if __name__=='__main__':
#多行输入
    import sys
    lines = []
    while True:
        line = sys.stdin.readline().strip()
        if line == "":
            break
        lines.append(line)
    # 单个取
    for item in lines:
        print(get_ans(int(item)))