fmt_scan = []


def main():
    n = next_int()
    m = int(n * 1.5)
    print(m)


def next_int():
    return int(next_str())


def next_str():
    if len(fmt_scan) == 0:
        for v in input().split()[::-1]:
            fmt_scan.append(v)
    res = fmt_scan[-1]
    fmt_scan.pop()
    return res


main()