1.2 KB | 1252 chars
"""
[11687: 팩토리얼 0의 개수](https://www.acmicpc.net/problem/11687)
Tier: Silver 1
Category: binary_search, math, number_theory
"""
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from datetime import datetime, timedelta
SYS_INPUT = True
RECURSION_LIMIT = 10 ** 7
SET_RECURSION = False
BLANK = " "
if SET_RECURSION:
sys.setrecursionlimit(RECURSION_LIMIT)
inp = lambda : sys.stdin.readline().rstrip() if SYS_INPUT else input()
mii = lambda : [*map(int,inp().split())]
mfi = lambda : [*map(float,inp().split())]
ii = lambda : int(inp())
fi = lambda : float(inp())
isplit = lambda : inp().split()
p = print
def gcd(a, b): return gcd(b, a % b) if b > 0 else a
def lcm(a, b): return a * b // gcd(a, b)
def get_five_cnt(num):
cnt = 0
k = 5
while num >= k:
cnt += num // k
k *= 5
return cnt
def solve():
n = ii()
INF = 1000 * n
left = 1
right = INF
ans = right
while left <= right:
mid = (left + right) // 2
cnt = get_five_cnt(mid)
if cnt > n:
right = mid - 1
elif cnt == n:
ans = min(ans, mid)
right = mid - 1
else:
left = mid + 1
p(ans if ans != INF else -1)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()