［AtCoder］ABC-143｜B - TAKOYAKI FESTIVAL 2019

設問ページ

• 🔗ABC-143 B - TAKOYAKI FESTIVAL 2019

提出結果

import itertools


def getInt():
    return int(input())


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


def main():
    n = getInt()
    d = getIntList()

    print(sum([x * y for x, y in itertools.combinations(d, 2)]))


if __name__ == "__main__":
    main()