#include <iostream>
#include <cstring>
#include <algorithm>
#include <cassert>
#include <cmath>
#include <vector>
#define fio(fn) freopen(fn".in", "r", stdin), freopen(fn".out", "w", stdout)
using namespace std;
using ll = long long;

ll n, x, y;
// chr_count, clipboard = time
//ll f[7005][7005];


int main()
{
//	fio("dice");
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
//	memset(f, 0x3f, sizeof f);
//	f[1][0] = 0;
	cin >> x >> y >> n;
//	n++;
	if (n == 1) {
		cout << "0\n";
		return 0;
	}
	ll ans = 0x3f3f3f3f3f3f3f3fll;
	for (int i = 1; ; i++) {
		ll a = floor(pow(n, 1. / i)), b = ceil(pow(n, 1. / i));
		vector<ll> pwra(i + 1), pwrb(i + 1);
		pwra[0] = pwrb[0] = 1;
		for (int j = 1; j <= i; j++) {
			pwra[j] = pwra[j - 1] * a;
			pwrb[j] = pwrb[j - 1] * b;
		}
		// 边界修正
		for (int j = 0; j <= i; j++) {
			if (pwra[j] * pwrb[i - j] >= n) {
				ans = min(ans,
					(x + y * (a - 1)) * j +
					(x + y * (b - 1)) * (i - j)
				);
			}
		}
		if (b <= 2) break;
	}
	cout << ans << '\n';
}