a = float(input())

ans = 1e20
for n in range(2,100):
  l,r = 0,100
  while r-l>1:
    m = (l+r)//2
    if pow(n,m) > a:
      r = m
    else:
      l = m
  if pow(n,r) > a and ans > n*r:
    ans = n*r

print(ans)