#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
  ll A, B;
  cin >> A >> B;
  ll N;
  cin >> N;
  if (N == 1) {
  	cout << "0\n";
  	return 0;
  }
  ll ans = 1LL << 61;
  for (int i = 1; i <= N; ++i) {
    ll root = ceil(pow(N, 1.0 / i));
    ll a = root, b = root + 1;
    vector<ll> powa(i + 1), powb(i + 1);
    powa[0] = powb[0] = 1;
    for (int j = 0; j < i; ++j) {
      powa[j + 1] = powa[j] * a;
      powb[j + 1] = powb[j] * b;
    }
    for (int j = 0; j <= i; ++j) {
      if (powa[j] * powb[i - j] >= N) {
        ans = min(ans, (a + b * (a - 1)) * j + (a + b * (b - 1)) * (i - j));
      }
    }
    if (root == 2) break;
  }
  cout << ans << '\n';
}