#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//const long nPrime = 1000000007;
//const long nPrime = 998244353;
typedef long long ll;
int main() {
    ll a,b,n;
    cin >> a >> b >> n;
    if(n == 1){
        cout << 0 << endl;
        return 0;
    }
    ll iNG = -1, iOK = 1e15;
    while(iOK-iNG > 1){
        ll iTmp = (iOK+iNG)/2;
        bool bOK = false;
        for(ll nA = 1; nA < 40; nA++){
            ll nB = (iTmp-nA*a)/b;
            if(nB < nA){
                continue;
            }
            ll p = nB/nA;
            ll q = nB%nA;
            ll nTmp = 1;
            for(ll i = 0; i < nA; i++){
                ll k = (i<q) ? (p+2) : p+1;
                if(nTmp >= (n+k-1)/k){
                    bOK = true;
                    break;
                }
                nTmp *= k;
            }
        }
        if(bOK){
            iOK = iTmp;
        } else {
            iNG = iTmp;
        }
    }
    
    cout << iOK <<endl;
    return 0;
}