백준 2292. 벌집

https://www.acmicpc.net/problem/2292

2292번: 벌집

N = int(input())

def f(N):
    if N == 1:
        return 1
    n = 1
    cnt = 1
    while True:
        n += 6 * cnt
        if N <= n:
            return cnt + 1
        cnt += 1

print(f(N))