import math, strutils, sequtils
var A, B: int
(A, B) = stdin.readline.split.map parseInt
var N = stdin.readline.parseInt
if N == 1:
  echo 0
  quit 0
var ans = high(int)
for i in 1..N:
  var
    a = int(floor(pow(float(N), 1 / i)))
    b = int(ceil(pow(float(N), 1 / i)))
  var powa, powb = newSeq[int](i + 1)
  powa[0] = 1
  powb[0] = 1
  for i in 1..i:
    powa[i] = powa[i - 1] * a
    powb[i] = powb[i - 1] * b
  for j in 0..i:
    if powa[j] * powb[i - j] >= N:
      ans = min(ans, (A + B * (a - 1)) * j + (A + B * (b - 1)) * (i - j))
  if b == 2:
    break
echo ans