#pragma GCC optimize("Ofast")
#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <ctime>
#include <assert.h>
#include <chrono>
#include <random>
#include <numeric>
#include <set>
#include <deque>
#include <stack>
#include <sstream>
#include <utility>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <tuple>
#include <array>
#include <bitset>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}
inline double time() {
    return static_cast<double>(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()) * 1e-9;
}



int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll A,B,N; cin >> A >> B >> N;
    if(N == 1){
        cout << 0 << endl;
        return 0;
    }
    vector<vector<ll>> dp(110,vector<ll>(50,-1));
    dp[0][1] = 1;
    for(int i=1;i<45;i++){
        for(int j=0;j<100;j++){
            if(dp[j][i] == -1)continue;
            for(int k=j;k<100;k++){
                dp[k][i+1] = max(dp[k][i+1], dp[j][i]+(ll)(k-j)*dp[j][i]);
            }
        }
    }
    ll res = (1LL<<60);
    for(int i=0;i<110;i++){
        for(int j=0;j<50;j++){
            if(dp[i][j] == -1)continue;
            if(dp[i][j] >= N) res = min(res, A*j+B*i);
            else{
                res = min(res, A*j+B*i+(N-1)/dp[i][j]*B);
            }
        }
    }
    cout << res << endl;
}