#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#ifndef LOCAL
#define file_name ""
#define csf                                                                               \
    {                                                                                     \
        std::cerr.setstate(std::ios_base::failbit);                                       \
        if (file_name != "")                                                              \
            freopen(file_name ".in", "r", stdin), freopen(file_name ".out", "w", stdout); \
    }
#define db(x)
#else
#define db(x) cerr << __FUNCTION__ << " L" << __LINE__ << " " << #x " = " << (x) << endl
#define csf
#endif
#define ll long long
#define unordered_map __gnu_pbds::gp_hash_table
#define f(x, y, z) for (ll x = (y); x <= (z); x++)
inline ll read();
using namespace std;
using __ = __int128;
const long long INF = 0x3f3f3f3f3f3f3f3f, M = 65;
ll n, a, b;
__ ans = INF;

bool check(ll x, ll y)
{ //?????
    ll a = y / x, b = y % x;

    __ res = 1;
    f(i, 1, x - b)
    {
        res *= a + 1;
        if (res > 1e18)
            return 1;
    }
    f(i, 1, b)
    {
        res *= a + 2;
        if (res > 1e18)
            return 1;
    }
    return res >= n;
}
signed main()
{
    csf;
    cin>>a>>b>>n;
    n--;

    f(i, 1, 65)
    { //?????

        ll l = i, r = n, mid, ans;
        while (l <= r)
        {
            mid = (l + r) / 2;
            if (check(i, mid))
            {
                ans = mid;
                r = mid - 1;
            }
            else
                l = mid + 1;
        }

        ::ans = min(::ans, (__)a * i + (__)b * ans);
    }
    cout << (ll)ans << endl;
    return 0;
}
/*
?????????

??????

????? 1 ????????? 3 ????23??????

????????????????w????v????????????v/w?????

???k???

???? x + k * y???? k + 1

x = 3, y = 1


k = 3

4 / 6

6 / 8

---------------

???????

???????

??????

???????????
*/